M14 Forum banner
Cancel
Create thread New Forums

308 Win reloads and my Polytech KABOOM!....

Jump to Latest
14K views 48 replies 17 participants last post by  jbrooks  
J
#1 · (Edited)
Did it really happen??

No. GI3

I just successfully survived a test in which I full-length resized and reloaded commercial 308 Win ammo through a side-stamped Polytech with maximum chamber... with no adverse effects.

Based on the assertions of some folks on this board that .308 Winchester fired in an oversize POS Polytech chamber are a recipe for disaster, I decided to test the assertion myself.

Now, I've been reloading for over 40 years, and much of that time have been wildcatting and fireforming brass to fit oddball European calibers. So I have a pretty good feel for headspace and brass failures. I know that I can safely fireform 30-06 to 9.3 x 62mm Mauser even thought he shoulder of the latter is forward of the 30-06 by a large margin.

Good Ol' Julian S. Hatcher, in his “Notebook” writes of reaming 30-06 chambers in such a way as to move the headspace forward by several hundreths of an inch with no problem.

So it really didn't bother me to fire regular .308 ammo in a Polytech chamber, even though the chamber almost swallows a 1.6455” M14 Field Reject gage...

Because the thing that really matters about headspace is not the actual dimension, but rather how well supported the base of the cartridge is. If the web of the case is not well supported by the bolt and chamber, then you may have issues. Things like blown extractors and splitting wood.

But so long as the web is supported, you can do just about anything with the shoulder and have no issues.

In case anybody wants to stop here, I'll give the summary. Due to the cost of components and time, I only used 5 factory rounds for this test... reloaded 4 times... Contributions are welcome if anybody wants me to continue this test.

Summary:

1. I First fired and then reloaded 5 commercial “308 Winchester” rounds (Remington) a total of 4 times. In other words, the cases had been fired a total of 5 times, including the initial firiing of the factory load.

2. Each time the brass was Full-Length resized, not using any special measures to accommodate the chamber dimensions. This is NOT necessarily good practice to maximize case life, but I wanted to stress the brass.

3. While reloading the brass for the 4th time, my decapping pin fell out and was lost in the grass, so only 4 cases were available for the fourth reload.

4. Upon firing the 4th set of reloads, I experienced a single case separation. A very common, non-dangerous condition that occurs often if you reload enough. I have experienced the same type of case separation with a factory FAL and the pics show that.

I trimmed the cases for the first reload and the 4th reload. No trimming was necessary in between.

Conclusion: The rifle and I survived the test, having used and reloaded commercial “308 Winchester” ammo in a Polytech that is supposed to blow up with anything but “7.62mm NATO” ammo. Absolutely no signs of head separation, weakening web, blown case head, or any other catastrophic failure....

In other words, shoot your stock Poly at will.... after you check the headspace...

************************************************************************


OK, so on to the test details:

The Rifle:

Polytech S/N 13xxx, According to Different this rifle was mad in April 1993.

Schmidt-Bender 1.5 - 4x scope, SA 4th Gen STEEL mount, Leupold QRW low rings.

The rifle is all stock Chicom with the following USGI parts:
1. Gas cylinder and piston
2. Trigger Group guts (H,T,S,safety, springs)
3. Op rod spring
4. Bolt ejector spring. All other parts of the bolt are original Chicom.

The rifle bolt has the typical out-of-spec lug size, and a USGI bolt will NOT drop into the rifle. I have fired about 500 rounds through this rifle so far with no change in headspace. Some folks mention rumors of “soft bolts” in these chicoms, but I disagree. Again, that's just me.

The headspace is such that the bolt “almost” closes on a Forster 1.6455” M14 Field Reject gage. In fact, the fired brass from this rifle measure 1.646”, so it is really at the MAX limit for headspace.

As for the Forster gage, it is good. I also use a Clymer 1.640” NO_GO gage as a double check and they are both good to go. My calipers are calibrated using ANSI Grade 0 Webber croblox gage blocks.

The ammo:

In a post a while back Gus had mentioned that Remington UMC is pretty poor brass. I couldn't locate any Rem-UMC, but did buy a box of Remington “308 Winchester” ammo with 147 grain FMJ bullet.

As it came from the box, the brass measured 1.628”, below 308 Win “GO”. Well within SAAMI, CIP and NATO specs.

My Pacific Durachrome dies full-length resized the brass to 1.629”.

The fired brass, coming out of the Poly chamber, measured 1.646”, a growth of 0.017”. EACH TIME I reloaded, the brass was squeezed back to it's original size, and each time it was fired it expanded 0.017”... yet required trimming only on the initial and 4th reload.

Now, I COULD have set the resizing die out about 0.01” to ease the working of the brass. But I wanted the brass to be resized fully in order to maximize the stress on the brass.

The components:

I had a stash of 147 grain FMJs and a few “junk” bullets, 170 grain round nose of unknown origin. So for the first 3 sets of reloads, I used the FMJs and the round nose bullets for the 4th and subsequent tests. All fed from the magazine with no problem.

I used about 43 grains of 4895 for everything (OK, maybe a bit stiff for the heavies, but I wanted to stress things. Use your own judgment when reloading...). I did NOT cut off the gas system but let the action cycle normally.

CCI 200 Large Rifle primers, hand-seated with an ancient Lyman 310 Tong Tool to BELOW the base of the cartridge. Just good practice.

Temp outside was 75 deg. F, and it was sunny so in the 2 hours for the test, things got hot to the touch.


The Process:

I Single-Loaded each round by placing it into the magazine and letting the op rod fly forward. I fully expected a case separation at some point, and I did not want to risk a live round being jammed into the stuck case from the preceding shot. NOT a safety issue, but I only had 5 rounds.

I marked each case with the reload number using a permanent marker. You will see the numbers 1,2,3,and 4 progressively down on the case. Each number denotes the times the case had been reloaded and fired. So... by the 4th reload, the case had been fired 5 times, including the original factory loaded case.

I propped an old shelter half next to the ejection port to catch the empties.

I also had an old Garand M3A1 Combination tool to use as a broken shell extractor. Good thing, too!

********************************************************************


The pics below and in following posts will add flavor to the story.

I'm glad I did this test, and was able to document it so.

To those who may quibble with “only 5 rounds”... well, take your pick. How many is a good mber? 100? 1,000? Certainly 5 rounds is in no way a valid “statistical test” but it was enough to convince me that the Polytech is just fine with commercial 308 ammo. Again, I am accepting contributions if anyone wants me to continue these tests.

I'll have a hell of a good time “testing” this rifle with your contributions!

Any counterarguments or statements that may contradict my findings should be first-hand and documented with pics as well...

JWB

PS... these initial pics show the mobile reloading unit (MRU), the test rifle and a summary pic of the 4th reload, compared to cmparable results from a factory FN FAL. The case separation of the M14 and FAL (in this case, Hornady TAP ammo) are classic cases of non-dangerous case failures from reloading. The succeeding posts will clarify.

It'sbedtime so I may defer additional posts/pics...
 
J
#2 · (Edited)
The progression of the reloads:

From Left to right:

1. After 1st reload, sized and primed

2. After 2nd reload, sized and primed

3. Before firing 4th reload, with round nose bullets. By now, the decapping pin had been lost so only 4 rounds were available.

4. The left case is the one that was not loaded for the 4th time. The next 3 are successful firings of the 4th reload, and you can see slight evidence of a ring around the case just above the number "4". The right case has failed but with no adverse effects to the rifle or shooter. This is a common result of case failure with many reloads.

ALL cases were full length sized at each reloading. Trimmed only ar reload No. 1 and 4.

I initially trimmed to 2.010". The cases exceeded 2.02" on the 3rd reload, so I trimmed them then.

JWB
 
#4 ·
Good to know; I have one with my WW2 SA Garand; will keep it handy when i hit the range with both of them. Thanks. GI1
 
  • Like
Reactions: jbrooks
Save
Reply Quote Like Like
A
#6 ·
thanks. BTW, I have a barrel that came off a Fed Ord M1A that will EASILY devour a Field Reject Guage that shot a few thousand rounds (according to the previous owner) with no problems whatsoever.

Likewise, here are a couple of gentleman who ran a reamer (IIRC) around 30-40 thousandths past GO and were whacking the firing pin with a pin punch and a 2x4 board to get enough contact with the primer to set the round off. Using 1943 headstamped brass! AGAIN (you guessed it), NO problems. They got PARTIAL case separation at .043 (FORTY-THREE thousandths past GO).. (BTW, I am pretty sure Bob Dunlap is Roy Dunlap's son--so this is not some hack smithie).

http://www.americangunsmith.com/vidlesson/?id=37d

The only "danger" from long headspace is if you get a case separation in COMBAT. Other than that, it's almost meaningless.
 
#7 ·
Questions:

1. I assume you were wearing shooting glasses when the one cartridge case separated? The reason I bring this up is because when such a thing happens, one can get eye damage from the gas or even a piece of cartridge case coming back into your eye.

2. I assume you were single loading/ single firing each round? IOW, there was not another live round fed into the chamber after the one case separated and the forward portion of the separated case still in the chamber? I would not want another live round fed into a chamber with the front portion of the separated cartridge case in there.

Separated cartridge cases in REAL M14's were so rare they were almost unknown in normal GI use. HOWEVER, that is because: 1. The barrels were annually inspected to ensure they did not exceed the Field Reject Headspace Gage 1.6445" in length. 2. The ammo was made to Mil Spec and in standard GI use, the ammo was fresh/unfired and never reloaded. (Some reloading was done by the Service teams for use in REAL NM M14 rifles, of course.) 3. Even in Field/Combat use the chambers were cleaned often enough so as not to add problems.

I was an Infantry Weapons Repairman MOS 2111 (Standard Military Armorer) when the 1st Marine Division still used the M14. The GySgt's and MSgt's then were those who had worked the M14 for the entire length of time we used the M14 up until we turned them in for M16A1's in 1972. They never even gave a hint of a suggestion that case separation was something we had to watch out for and I never heard a hint of a suggestion that any Range Armorer had run into it. We did not have a ruptured cartridge case extractor as part of the standard Armorer's Tool Box, though they may have added them to Range Armoer's Tool Boxes and especially in combat areas. I actually never even SAW a ruptured cartridge case extactor for the M14 UNTIL I became an RTE Repairman MOS 2112 (NM Armorer).

Now AFTER I became a NM Armorer, I sure did see ruptured cartridge cases in Commercial M14's in use by civilians, though we almost never had to use them in REAL M14's even when we used reloaded ammo. Of course, we ONLY reloaded ammo TWICE and then turned the cases in for salvage because we did not want the possibility of a ruptered cartridge cas in our rifles.
 
J
#8 ·
Gus Fisher said:
Questions:

1. I assume you were wearing shooting glasses when the one cartridge case separated? The reason I bring this up is because when such a thing happens, one can get eye damage from the gas or even a piece of cartridge case coming back into your eye.

I was wearing glasses, but not shooting glasses. This kind of failure will NOT result in pieces of brass going anywhere. but out the ejection port.

2. I assume you were single loading/ single firing each round? IOW, there was not another live round fed into the chamber after the one case separated and the forward portion of the separated case still in the chamber? I would not want another live round fed into a chamber with the front portion of the separated cartridge case in there.

As I mentioned, I single loaded each round. I fully expected a case separation at some point. I have had many with reloads. They are harmless, but they do jam up the rifle when the next round attempts to chamber.

Separated cartridge cases in REAL M14's were so rare they were almost unknown in normal GI use. HOWEVER, that is because: 1. The barrels were annually inspected to ensure they did not exceed the Field Reject Headspace Gage 1.6445" in length. 2. The ammo was made to Mil Spec and in standard GI use, the ammo was fresh/unfired and never reloaded. (Some reloading was done by the Service teams for use in REAL NM M14 rifles, of course.) 3. Even in Field/Combat use the chambers were cleaned often enough so as not to add problems.

Yes, this would never happen in the military, they use fresh ammo. If this ever did happen, it would mean really crappy lot of brass. I wanted to show that I did not self-destruct when firing "308 Win ammo, but the reloads were pure gravy. GI1

I was an Infantry Weapons Repairman MOS 2111 (Standard Military Armorer) when the 1st Marine Division still used the M14. The GySgt's and MSgt's then were those who had worked the M14 for the entire length of time we used the M14 up until we turned them in for M16A1's in 1972. They never even gave a hint of a suggestion that case separation was something we had to watch out for and I never heard a hint of a suggestion that any Range Armorer had run into it. We did not have a ruptured cartridge case extractor as part of the standard Armorer's Tool Box, though they may have added them to Range Armoer's Tool Boxes and especially in combat areas. I actually never even SAW a ruptured cartridge case extactor for the M14 UNTIL I became an RTE Repairman MOS 2112 (NM Armorer).

Now AFTER I became a NM Armorer, I sure did see ruptured cartridge cases in Commercial M14's in use by civilians, though we almost never had to use them in REAL M14's even when we used reloaded ammo. Of course, we ONLY reloaded ammo TWICE and then turned the cases in for salvage because we did not want the possibility of a ruptered cartridge cas in our rifles.
Click to expand...
Thanks, Gus, again, I wouldn't expect ruptured cases from factory ammo. If you reloaded the match ammo twice, I think that is a good number.

A ruptured case during a match will certainly jam the rifle and make for a bad day.

JWB
 
A
#12 ·
gregaba said:
I used the M14 in combat in nam and don't know how many thousands of rounds I fired though it but went though 3 barrells in my time there. I never had a case failure including the M60 ammo we had to use a few times when things got hot and we ran out of regular ammo.
Greg
Click to expand...
not sure what folks told you at the time, but, as far as I know, there isn't any such thing as "M-60" ammo. The M60 ammo cans (linked) would typically be loaded with (mostly) four M80 Ball and then 1 Tracer. I don't recall personally shooting linked AP/Tracer, but I am sure it exists (suspect it is/was more likely used in Armored/Mech units).
 
#14 ·
We bought a LOT of stuff from Herter's back in the 60's including, GASP, SHOCK, THE HORROR, a .22 Mag Marlin Rifle I saved up for and Dad ordered for me THROUGH THE MAIL before the 1968 Gun Control Act.

I am VERY glad we normally have enough ammo supplies nowadays that we don't have to even consider reloading in combat, though there was at least one time a forward deployed Marine Unit in Afghanistan ran out of ammo when they got into a protracted fire fight and wound up resorting to the bayonet before they got help and resupplies.
 
#15 ·
I'm really glad you did this test to disprove some of what's been reported.
I don't claim to be a "expert" in reloading, but I have been doing it for over 30 years and I have learned a thing or two in my experiences.
I have seen my share of misinformation concerning hand loading ammo here from so called "knowledgeable" people. I don't call them out normally on their misinformation, in order to avoid a argument. I don't need the aggravation.
Great test!!
 
#16 ·
Well I'm no exspert, I just like too think I am. I have always said 4 reloads and the brass is done what I am surprised is that JWB didn't get CHS sooner with the generous chamber lenth of his rifle using commercial brass.

Personally I'm not sold on the X-die or its claim too extend brass life, I would like too see the same experiment done with one.
 
J
#23 ·
Sometimes this is due to certain laws in some countries that outlaw "military calibers" like 7.62mm NATO but permit hunting ammo like 308 Win. The imported FN/FAL, for example, is marked the same.

Laws are usually written by complete idiots... regardless of the country.

JWB
 
J
#22 ·
Thought I'd share this as long as we're talking about reloading and case failure.

This is a Norma 9.3 x 62mm case. I bought a rifle in that caliber when I was stationed in Germany in 1982... I had the rifle, a custom Model 98, built by Waffen Bender in Zuzenhausen. Outstanding caliber for just about anything on the planet.

For perspective, the case head is identical in size to the 30-06. (+/- a couple thou...)

I bought 2 boxes of "used" brass and began reloading, using loads suggested by Finn Aagaard in the American Rifleman (I forget the date...). I reloaded the same brass maybe 15 times. Yes, no joke. With a tight chamber and bolt action, and moderate loads, you can get an awful lot of life from brass.

A couple years ago I loaded this case and fired it. Later, as I was sorting the brass and checking it all as I always do, I found this incipient head separation.

This head separation had zero effect on anything. But the line on this case delineates the rupture area of a 30-06 type case that could become problematic. If the case head is not fully supported below this area, then you risk a catastrophic failure. But this would be readily obvious when you look at the bolt and chamber relationship.

JWB
 
#24 ·
I would like to mention my main problems with Remington UMC ammo is spotty accuracy and not as much uniformity of function that I want to see for a "Gas Gun." I have mentioned it seems to have more extractor damage than other brass, but as I have also mentioned, I only use UMC when I can't get my hands on other ammo that is "paramilitary quality" or specifically made for "Gas Guns." I have not run into any case separations or any other signs of weakness or potential problems after firing the rounds and examining the cartridge cases that would lead me to think the cartridge brass is unsafe or really poor quality. Again, the main reason I don't like UMC is poorer accuracy compared to other paramilitary ammo and sometimes it doesn't function the rifle as uniformly as I would like. I have not run into these problems with .30-06 or .308/7.62mm Federal American Eagle or Winchester White Box ammo and is why I recommend them.

JWB noted he did not use UMC ammo, but he did use Remington ammo/cases. I do not know if Remington uses exactly the same brass in their UMC ammo as their regular ammo. However, I do want to mention again I never saw reason to even suspect that UMC cases were weak in the area that cartridge cases normally rupture when they do rupture. I ALSO want to make a point that I don't know how many civilian shooers, percentage wise, were reloading Remington Cases for NM usage. I DO know the civilian shooters who shot at Quantico and other places Marine Shooters were competing, were quick to pick up the free Federal and GI Lake City NM ammo cases to reload as well as many of them used surplus GI 7.62mm cases.

As a NM Team Armorer for a Post and StationTeam, a NM Armorer for the BIG USMC Team, as a NM Armorer for at least 6 Division Matches where the NM M14 was fired and at least two, if not three Marine Corps Matches where the NM M14 was used, and I have forgotten how many "Civilian Sponsored" NM matches; I have seen more ammo run through more real M14's and commerciall M14's than a whole lot of people. Even at a SMALL Division Match, there was always at least 175 shooters firing at least 60 rounds a day for 15 days and that makes at least 157,500 rounds fired even at a small Division Match. During a Summer Team with THE Marine Corps Rifle Team, we had 60 shooters firng AT LEAST 120 rounds a day every day between May 20 and August 15 with the exception of days we actually only fired one NMC during matches and the ONE day we got off on the 4th of July. So in one of those years, I witnessed over a Half a Million rounds fired through Marine Corps M14's alone, besides what other Teams and civilians fired. IOW, I can only GUESS at how many MILLIONS of rounds I saw fired through NM M14's and Commercial M14's in my career.

Now, as a NM Armorer, we were informed of ALL the gun and ammo problems on our Teams or at the Division Matches as well as what we personally witnessed shot by Marines, other Service Team Shooters and Civilian Shooters while "Walking the Line" during rapid fire and even slow fire stages at matches. IOW, virtually NO individual shooter could hope to see or learn the results of anywhere close to what a NM Armorer with years of experience around NM M14's and NM Commercial M14's has seen. I admit I sometimes get frustrated or shake my head when I hear or read something can "never" happen and I have personally witnessed it or heard or read ffrom reliable sources where something DID happen and that supposedly "could never" happen. That's when I think that perhaps when someone who makes such a statement has not even seen his/her first million rounds fired out of these rifles llet alone a second, or third million or more rounds fired.

For example, how many people have ever seen a REAL GI M14 blow up or even been on the range or shooting facility when it happened? Well, you can count those involved at Springfield Arsenal who did the "firing to destruction tests" add that is not many people. Outside of them, there were probably very few people in that category. I did not see the M14 blow up as I was on the other side of the firing line when it happened and there were fewer than 60 people on the range that day. However, many of us support personnel and other Team Members rushed over to give medical assitance and of course we Armorers collected the pieces of the rifle and began the initial inspection pending the full investigation. I DO want to state the cause was NOT from excessive headspace, but rather the WRONG kind of barrel steel used in a NM barrel made by a well respected Commercial NM barrel maker. He PAID for quality and guaranteed steel to make the barrels from, but GOT poor quality steel with sulphur stringers in it.

OK, it is very late and I am too tired to type more tonight, so I will continue this post in the next day or so.
 
J
#26 ·
As an aside, brass will stretch radially a fair amount before rupturing, but I certainly didn't try to size the base back to it's original size for another full expansion test!

Shortened and shoulder bumped .303 British brass in a 7.62x54r with the regular 7.62x54r load:

Image


.30-30 in the Russian rifle didn't do so well, though:

Image

The .30-30 is on the far right. It might have survived had it been better centered.

Brass is used because it can take a lot of abuse. It just may not do it multiple times!
 
J
#27 ·
Good pics, jmoore...

The 308 I fired had no real expansion at the web. The rear part of the ruptured case measures 0.472" at the widest part and is consistent all the way around. A new round from the same box measures 0.466" at the base of the case just above the rim. SO the chamber only permitted a minimum of expansion. There is absolutely zero evidence of bulging of any sort that may be indicative of poor support of the web.

Here is a close-up of the rear portion... no discernable bulge..

JWB
 
#28 ·
OK, now that I may have risked boring the crap out of many forum members by writing so much in my last post, let's see if I can finish my points in this post.

First I would like to address little pieces of cartridge brass coming back into a shooter's face and possibly his/her eyeballs. BOTH the M1 Garand and M14 are top ejecting rifles and even with new GI ammo and GI Garands or REAL M14's, you will sometimes get little pieces of the brass coming back into your face. MOST of the time this can be traced to an extractor that has a sharp lip or somehow got dinged and is shaving a little brass off the case. I wasn't trained to watch for that as a standard Infantry Armorer, but we were trained to look for it in NM rifles. In some of the "worst case examples," if you see either type of rifle that shows what looks like gold flakes accumulating in the magazine/clip well, then special attention should be addressed to BOTH the ammo and the extractor. Often, a burr or sharp edge on the extractor causes it and stoning will get rid of the problem. However, M1 and M14 rifles with good ammo and good extractors WILL occasionally throw small pieces or flakes of cartridge brass back onto the shooter's face or eyeballs.

Now I don't want to overly alarm people about this and I'm not tryng to use scare tactics. Most of the time people get little pieces of cartridge brss in their eyes, they can pick them out or tears and water will wash them out. There were a few times in my career that the shooter had to be taken to see a Doctor to have the brass spec removed from a shooter's eyes, though. Of course, shooting glasses is the best method of protecting our eyes for most shooting and those of us who wear prescription glasses, will most of the time also have some/decent eye protection for this.

OK, so let's take this a step further to when a cartirdge case ruptures. MOST of the time, the cartridge case will crack a little or a lot, but not separate into two pieces. However, when a cartridge case actually cracks in two pieces, a little piece of cartridge brass can also crack off and wind up in the shooter's eyeball. This normally happens when the rear piece of the case is ejected and hits the receiver or the op rod. I want to ensure people understand this DARN SURE can happen because it HAS happened before. Of course, an inbestment in a good pair of shooting glasses or tempered prescription glasses will pretty much ensure it won't happen to you.

Now the next point about gas coming back into your face when a cartridge case ruptures enough or breaks in two pieces. It is not so much the gas that can be detrimental to your eyeballs, but rather the pieces of unburned powder or foreign matter that gets thrown back in your face. Again, good shooting glasses will protect your eyes.

Now, if a person wants to ignore these safety warnings, that is totally up to them. From personal experience, there have been times I was DARN glad I was wearing some kind of eye protection when shooting these rifles and I have seen it save larger problems with others.

OK, now back to the intent of the original post.

I am not sure where JWB got the idea that an M14 or M1 would "blow up" or cause a huge "KABOOM" when the headspace IS inside the safe headspace limits and American brass is used from a well known company, because that was what happened in this investigation from his own reported information By what he wrote, the headspace was LONG, but not unsafe when checked with the Field Reject Gage.

I would submit that though this test is not large enough by any measure to be considered a scientific sampling, the information from this test goes along with what most of us are saying, I.E. "If your headspace is LONG, then ensure you are using Good Nato Spec or American Made brass and watch how many times you reload the cases."

I could be mistaken, but that is what I get out of this test.
 
J
#29 · (Edited)
Gus Fisher said:
...I am not sure where JWB got the idea that an M14 or M1 would "blow up" or cause a huge "KABOOM" when the headspace IS inside the safe headspace limits ....
Click to expand...
That's the point... they are not inside the specs for .308 Win...

I don't need to go into the multitude of posts where the "differences" between "308 Win" and "7.62mm NATO" have been debated. A casual search of this forum will tell the story. And a thoughtful consideration of the SAAMI and NATO specs will reveal there are no differences in the ammo. But that's not the accepted position of many on this board.

I conducted this test as a response to many of those posts. I announced my intent many times over the past months but finally had the opportunity to do it.

Since the SAAMI Field Reject for .308 Win is certainly not 1.6455", but 1.640", the Polytech EXCEEDS the Field Reject for 308 Win. It swallows the 1.640" gage with room to spare. Hence, must be UNSAFE for that round, according to many experts.

That was the whole point of my test. The Poly exceeds the specs for "308 wIN", so must be DANGEROUS for that ammo... but we see that is not the case... the stock Polytech is just fine for 308 Winchester.

In addition, not only did the 308 Win fire successfully the first time, in an out-of-spec chamber, but I got at least 3 MORE RELOADS out of the brass after full-length resizing. That was pure gravy, and frankly, exceeds the popular belief that a Poly is unsafe with 308 Win ammo under any conditions. Why the immediate response to a new Poly owner to get a "USGI bolt conversion" from many on this forum?

No need for those expensive "bolt conversions"IMO.

In addition, there is a very large safety factor as far as headspace specs are concerned. jmoore's post goes a long way in that direction. Simple HS measurements are not the "rest of the story".

Once again, I'll gladly accept contributions of components in order to conduct a more "scientific" test. DI2 Results will be duly posted.

And once again, documented evidence to the contrary , not anecdotal stories, is welcome.

JWB
 
#30 ·
You keep saying that the SAAMI Field Reject is 1.640 and yet ALL SAMMI Field Reject Gages are 1.638." I don't know why SAMMI publishes a blueprint with a supposed Field Reject longer than the gage they certify, but they do.

The danger of excessive headspace is in the fact a poor quality or too hot cartridge can rupture and thus hot gas and/or foreign matter will be blown back into the shooter's eyeball/s with loads that are correct for the rifle. ALSO, many types of .308 win. rounds are NOT suitable to shoot in even an M1A that headspaces within the Field Reject limit of 1.638."
i am not suggesting you were trying to say that, but it is important to get it across to forum members so they don't shoot over pressure hunting ammo, for example.

Please don' take this as an insult, but five cases fired and reloaded and fired four more times is far from any kind of statistical sample that can be used for proof of anything. Only a much, much larger sample of more ammo in a lot more rifles would be definitive proof of anything because your sample does not even take into account that in any large batch of ammunition, there is going to be some that have defects that may not or probably not noticeable until they are actually fired.
 
J
#31 · (Edited)
Gus Fisher said:
You keep saying that the SAAMI Field Reject is 1.640 and yet ALL SAMMI Field Reject Gages are 1.638." I don't know why SAMMI publishes a blueprint with a supposed Field Reject longer than the gage they certify, but they do.


The SAAMI max chamber is 1.640" (41.66mm) as can be seen at the SAAMI page.

Page 66 of
http://saami.org/specifications_and_information/publications/download/206.pdf

If the SAAMI Field Reject gage is 1.638", then that means that SAAMI accepts chambers that are beyond the Field Reject gage. In other words, that means SAAMI sanctions out-of-spec chambers as part of their drawing.

I don't believe that.

Let's quote a page from Clymer Catalog (I believe you respect Clymer HS gages...):
Page 12 of:

http://www.clymertool.com/catalogue/ClymerCatalogueVol11.pdf

Quote:

"Clymer "GO" and "FIELD" gages correspond to the SAAMI minimum and maximum respectively. " ...

"Because many feel that .010” is too much variation between a minimum and maximum chamber, we also offer as standard a “NO-GO” gauge, which is .006” longer than our “GO”." (1.636" for "NO_GO")

Now, the SAAMI min chamber is 1.630" and the max is 1.640". So that tells me that Clymer Field Reject id 1.640". Perhaps somebody can show us a pic of a Clymer Field Reject gage that is etched with the size, either 1.638" or 1.640". That would be interesting.



The danger of excessive headspace is in the fact a poor quality or too hot cartridge can rupture and thus hot gas and/or foreign matter will be blown back into the shooter's eyeball/s with loads that are correct for the rifle. No. Simply not plausible with US commercial ammo. ALSO, many types of .308 win. rounds are NOT suitable to shoot in even an M1A that headspaces within the Field Reject limit of 1.638."

Well, check out post No. 1 here:

http://m14forum.com/ammunition/59716-springfield-armory-ammo-recommendations.html

Quote:

"You may use any factory .308 ammunition made to SAAMI spec."

Includes even 308 Hornady Lt Magnum for occasional use. The list of SAI recommended ammo seems to cover the waterfront as far as commercial hunting ammo goes. Perhaps there is a single exception to the US commercial ammo here, but I don't see it.


i am not suggesting you were trying to say that, but it is important to get it across to forum members so they don't shoot over pressure hunting ammo, for example.

Please don' take this as an insult, but five cases fired and reloaded and fired four more times is far from any kind of statistical sample that can be used for proof of anything. Only a much, much larger sample of more ammo in a lot more rifles would be definitive proof of anything because your sample does not even take into account that in any large batch of ammunition, there is going to be some that have defects that may not or probably not noticeable until they are actually fired.

No problem Gus, I don't get insulted very easily. But I said at least 3 times in this thread that my test was neither scientific nor statistically valid. But I am quite convinced that the supposed issues with HS, short or long, are not nearly as dramatic as many woould have us believe.
Click to expand...
But let's get back to your premise of 1.638" as the SAAMI Field Reject. If that is the case, then MY chamber is 0.007" TOO LONG and very Far outside SAAMI safe specs. But I had no problems with the commercial ammo and reloads. Didn't even come close.

Bottom line, IMO: No need to pick the nits out of HS specs with the M1A/M14 clones. Use common sense in your reloading and use ANY US commercial 308 ammo in your favorite rifle.

As a reminder, this thread is about the Polytech and their long chambers. I'm certainly no advocating purposely reaming an M1a barrel just for the purpose of enlarging headspace...

JWB
 
J
#36 ·
AKA hit the nail on the head, and said it probably better than I would have...

Recall, I Full Length resized the brass so it could be used in any rifle. The average match shooter will custom size the brass for use in that ONE rifle for matches. In which case, there is absolutely zero difference in case life.

As for pressure, there is no difference in spite of allegations by some on this board. The pressure is governed by the laws of thermodynamics and interior ballistics. There is a formula called "Le Duc" formula that has been in common use by the ballistics community since the 1800s. That still holds (physics hasn't changed over the years...). But it's way to involved to get into here.

JWB
 
A
#38 · (Edited)
there is no such thing as "hot" (commercial) hunting loads. ALL of it will be under (likely WELL under) SAAMI max pressure. Some ammo (i.e. "ultra-performance" type ammo) use proprietary powders (slower) to develop greater velocities. Whether ANY of these loads would over-tax the SELF-REGULATING gas system of an M1A/M14, who knows (I doubt it, at least with 150 grain bullets).

Likewise, I am (deeply) skeptical regrading how one could allegedly "wear out" an M14 receiver "faster" than a bolt gun. M1/M14 receivers typically don't "wear out" until you get into the 100,000+++ realm. Even with "warm" long-range loads, I doubt you could increase the wear out factor much more than say 10%?? If so, "one or two years" ain't gonna do it (unless you shoot 6 days a week from sun-up to sundown).

The M14 (or well made M1A) receiver is EASILY as "strong" and durable as most any commercial bolt gun.

(PS-ADDED: BTW, feel free to read/refer to Hatcher where John Garand himself tested the strength of the receiver by shooting vast quantities of PROOFING rounds in an M1. Finally one of the bolt lugs failed. Guess what, they KEPT ON SHOOTING the thing until everyone got bored and went home--no mention was made of any other "damage" or excess wear to op-rod, etc. So much for being "oblivious" to the comparative strength of bolt guns vs. M1?M14s--lol).

Oh yeah, the "Nato Spec" and the SAAMI maximum spec, when correlated for the differences between CUP and PSI are essentially the same..
 
#40 ·
AKA Hugh Uno said:
there is no such thing as "hot" (commercial) hunting loads. ALL of it will be under (likely WELL under) SAAMI max pressure. Some ammo (i.e. "ultra-performance" type ammo) use proprietary powders (slower) to develop greater velocities. Whether ANY of these loads would over-tax the SELF-REGULATING gas system of an M1A/M14, who knows (I doubt it, at least with 150 grain bullets).

Likewise, I am (deeply) skeptical regrading how one could allegedly "wear out" an M14 receiver "faster" than a bolt gun. M1/M14 receivers typically don't "wear out" until you get into the 100,000+++ realm. Even with "warm" long-range loads, I doubt you could increase the wear out factor much more than say 10%?? If so, "one or two years" ain't gonna do it (unless you shoot 6 days a week from sun-up to sundown).

The M14 receiver is EASILY as "strong" and durable as most any commercial bolt gun.

Oh yeah, the "Nato Spec" and the SAAMI maximum spec, when correlated for the differences between CIP and PSI are essentially the same..
Click to expand...
You have the right to believe anything you wish to believe about GI M14's with how much experience do you have with them and hot ammo?

It is not just a matter of total PSI of the cartridge, but also the pressure curve (or how soon the pressure peaks) that can and will cause problems.

To suggest an M14 is as strong as a bolt action is well, simply oblivious of the mechanical strength of each receiver.
 
J
#39 · (Edited)
So let's get back onto the subject of this thread...

A Polytech with very long headspace was successfully fired with commercial 308 ammo.

No issues.

Same Polytech with very long chamber also successfully fired reloaded commercial ammo that was full-length resized.

No issues.

The relationship of this test to any REAL M14s is of no relevance, nor is current practice in the military regarding EBRs.

Quibbl9ing over small differences in headspace gages or specs has no bearing on the results of the test.

The test was not, nor was it intended to be, a scientific or rigorous endeavor. Stated up front.

Interpret the results of the test any way you wish. Doesn't change the results.

There is a HUGE amount of misleading, biased and otherwise incorrect information on the web regarding the entire 308 vs 7.62mm NATO "differences". On this forum and every other forum.

ONCE AGAIN.... Any documented and verifiable evidence which may be contrary to my results is welcome.

So far, that evidence is sorely lacking. This thread has been viewed by over 1,700 members...so far no contravening evidence...

JWB
 
#42 ·
jbrooks said:
So let's get back onto the subject of this thread...

A Polytech with very long headspace was successfully fired with commercial 308 ammo.

No issues.

Same Polytech with very long chamber also successfully fired reloaded commercial ammo that was full-length resized.

No issues.

The relationship of this test to any REAL M14s is of no relevance, nor is current practice in the military regarding EBRs.

Quibbl9ing over small differences in headspace gages or specs has no bearing on the results of the test.

The test was not, nor was it intended to be, a scientific or rigorous endeavor. Stated up front.

Interpret the results of the test any way you wish. Doesn't change the results.

There is a HUGE amount of misleading, biased and otherwise incorrect information on the web regarding the entire 308 vs 7.62mm NATO "differences". On this forum and every other forum.

ONCE AGAIN.... Any documented and verifiable evidence which may be contrary to my results is welcome.

So far, that evidence is sorely lacking. This thread has been viewed by over 1,700 members...so far no contravening evidence...
JWB
Click to expand...
Documented evidence against what you are proposing was brought up by, well, YOU when you showed that SAAMI says the Field Reject limit for the .308 is about .004" less then the chamber in your rifle. You seem to have ignored this fact, yet again.

You are arguing against SAAMI's interpretation of what the maximum headspace should be for .308. Can anyone here document how they came to that conclusion? Probably not. Was that standard taken from only firing a few cartridges in ONE rifle? Probably not.

For this argument to be proof of anything, you would have to document how SAAMi's interpretation of the maximum headspace for .308 is wrong and you have never demonstrated that.
 
J
#43 ·
And introducing unwarranted fear about a firearm's capabilities is not wise. How exactly can a person get hurt by firing 308 ammo in a long Poly chamber?

Please explain the physics...

Oh... yes, there are folks here who speak in very general terms about "energy waves"..."back thrust"... and other terms that have no basis in physics...

I hear a lot of "would"..."Could"... "WILL DEfinitely"...

I keep waiting for evidence from other folks who have fired 308 in a Poly to relate their documented cases of blown bolts, brass in eyes, etc.

I'm still accepting donations of components so I can continue my tests... GI1

JWB
 
M14 Forum
posts
2.7M
members
67K
Since
2002
A forum community dedicated to M14 and M1A Rifle owners and enthusiasts. Come join the discussion about optics, ammunition, gunsmithing, styles, reviews, accessories, Modern, Devine, SOCOM, EBR, classifieds, and more!
Full Forum Listing
Explore Our Forums
The M14 Ammunition Modern M14 Gun Rights New Member Introductions