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Anomalous procedures..

This is a discussion on Anomalous procedures.. within the Art Luppino forums, part of the Gun Professionals category; Most procedures for doing M1A/M14 modifications are learned procedures, someone else developed them, and they passed on until titled Normal Procedures. History tells a somewhat ...


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Old August 23rd, 2016, 04:51 AM   #1
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Anomalous procedures..

Most procedures for doing M1A/M14 modifications are learned procedures, someone else developed them, and they passed on until titled Normal Procedures.

History tells a somewhat different story that is far more interesting.. Interest is the key word for many people that enjoy making or doing things themselves. This interest is the beginning. The greatest pleasure is to overcome situations that are beyond the individuals skills or lack of equipment, which brings me to the current point..

" Barrel Gas Port location." Referring to the M1A..

The gas port location has long been established, as well the reasons why. An Earlier Thread, "Experimental Barrel Project", changes the gas port location norm. The location change is necessary if the rifle is to shoot in a semi mode..

Concern to follow established data is not part of the objective, keep that in mind please if you decide to respond. It would be more valuable to hear ideas out side the box, Anomaly; n, departure from the usual.

The issue at hand is the gas port location inside the Barrel related to the rifling.. The location question is. If the Gas Port does not reside in the barrel land what is the significance?

It is this Historical Port location that determines measurements for location of other parts. I do not believe that is a hard and fast rule to produce a barrel that gives acceptable accuracy.

Can anyone produce evidence otherwise? Art L.

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Old August 23rd, 2016, 05:11 AM   #2
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Personally I don't really believe that the G/P need be in the "Land" I think that may just be a Krieger thing and why they won't turn a 5R tube in a M14 contour when 2 other cut barrel makers and 2 button makers will.

I have often wondered myself how well a M14/M1a would perform if the G/P was relocated too the front leg of its G/C, much like the Long Range shooters do with the AR/M16 rifle? Is that what your thinking, Art ?

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Old August 23rd, 2016, 05:31 AM   #3
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Gas port

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Originally Posted by Phil McGrath View Post
Personally I don't really believe that the G/P need be in the "Land" I think that may just be a Krieger thing and why they won't turn a 5R tube in a M14 contour when 2 other cut barrel makers and 2 button makers will.

I have often wondered myself how well a M14/M1a would perform if the G/P was relocated too the front leg of its G/C, much like the Long Range shooters do with the AR/M16 rifle? Is that what your thinking, Art ?
Phil,

I've done both things you mentioned, once locating the gas port at the front of the cyl, down through the lock and plug, driving the piston from the front, and many times drilling the barrel port after desired Cyl location, none of which located in the lands.. Both of these mods proved to be excellent rifles..

What I would like to have is evidence of why not to... Art

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Old August 23rd, 2016, 05:48 AM   #4
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I have no negative evidence. But there may be some considerations. My guesses: The gas port is located in a particular place on the length of a barrel where the gas pressure and volume of a particular cartridge are compatible with the whole system design. Conventional designs place the port on the top or bottom of a barrel but usually in a groove. Not being an engineer or a firearms designer, I can only guess at a reason. Since the lands have a smaller I.D. and engrave the projectile the leading edge of the land stands a greater chance of collecting bullet material which may or would restrict the gas flow if the port does not stay at optimum size. That may require more inspection and maintainance to keep clean, but should not have any real detrimental effect on accuracy - provided that the port does not mar or remove enough bullet material to unbalance it. That may be the trick - how to round the port at its intersection with the bore to prevent it from picking up bullet material that would unbalance the projo. If the projo is spinning at 200K to 250K RPM it should be relatively stable for several hundred yards. Displacing the port 1/10" may result in a port that intersects the bore at a half-land / half-groove location which is not optimum. I don't know how you would go about satisfactorily plugging the old port in order to drill a new one in an original position. I'm sure that there are modern welding techniques that I am ignorant of. Just some food for thought. Oh, and how do you define "acceptable accuracy"? It will be interesting to follow what you do.

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Old August 23rd, 2016, 06:00 AM   #5
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edit at 16:35 EDT: I seem to have gotten my barrel land/groove terminology confused, and used inconsistently ....
In the tesx below I've updated (hopefully correctly) to use the term 'GROOVE' to be the part of the barrel rifling with the largest diameter, and 'LAND' for the smaller diameter sections. The barrel is initially bored for the (smaller) diameter of the LANDs, and then 'rifled' to produce the (larger) GROOVEs - e.g. a 308Win barrel typically has a bore/LAND diameter of 0.300 and a GROOVE diameter of 0.308 .

No 'evidence', but my thought is that having the gas port in a GROOVE just 'seems like' the location that would cause the least problems.
And from an aesthetics view - it just 'looks nice'.

There might be machining concerns about drilling a precisely dimensioned hole if the location is partially land & groove - due to tool drift.
Having the port in a LAND would also result in it having greater (deeper) contact with the bullet's outer surface.

Without 'knowing' that those items aren't important, the 'safe decision' is to place the port in a GROOVE.

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Endwell NY USA

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Old August 23rd, 2016, 11:23 AM   #6
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Back when I was shooting with the National Guard I was told by the folks at the NGMTU that it was desirable to have the gas port located in the rifling groove. This was from the result of testing conducted at the ARMTU, Ft. Benning. They claimed that having the port located within the groove resulted in a slight accuracy benefit. We felt we could use all the help we could get...

I check all of the barrels that come into my shop for gas port location. Most Krieger barrels have been in the groove. Less than half of the Criterion barrels have been in the groove. I'm not a good enough shot anymore to realize the difference. I have found that it makes no difference in .223 barrels. I'm still a little uncomfortable with those that have the port half in and half out. I think it needs to be either directly on the land or in the groove.

The problem with the gas port is that drilling the port leaves a small burr in the barrel that causes copper fowling. I'm at a loss to describe how this effects accuracy other than that we know copper fowling is detrimental to accuracy. Part of the new barrel break in procedure is designed to eliminate the burr around the throat as well as the gas port. In theory, this helps improve accuracy.

Hey Art, please stop using those big words... It messes with my mind - what's left of it.

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Old August 23rd, 2016, 11:26 AM   #7
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Krieger puts the port hole in a groove, not a land. It's a bigger target.

I've seen (and had) many other barrels with the port randomly located, often partially in a groove and on a land. Shooting in competition, I never could tell the difference.

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Old August 23rd, 2016, 11:44 AM   #8
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OK just for you

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Back when I was shooting with the National Guard I was told by the folks at the NGMTU that it was desirable to have the gas port located in the rifling groove. This was from the result of testing conducted at the ARMTU, Ft. Benning. They claimed that having the port located within the groove resulted in a slight accuracy benefit. We felt we could use all the help we could get...

I check all of the barrels that come into my shop for gas port location. Most Krieger barrels have been in the groove. Less than half of the Criterion barrels have been in the groove. I'm not a good enough shot anymore to realize the difference. I have found that it makes no difference in .223 barrels. I'm still a little uncomfortable with those that have the port half in and half out. I think it needs to be either directly on the land or in the groove.

The problem with the gas port is that drilling the port leaves a small burr in the barrel that causes copper fowling. I'm at a loss to describe how this effects accuracy other than that we know copper fowling is detrimental to accuracy. Part of the new barrel break in procedure is designed to eliminate the burr around the throat as well as the gas port. In theory, this helps improve accuracy.

Hey Art, please stop using those big words... It messes with my mind - what's left of it.

The possibility of a burr in the barrel exists, if it messes with stuff does not exist. Using several patches and pulling them through the bore never gave any indication of a snag while passing over the drilled port, That doesn't mean a whole lot either. Maybe someone could recover a bullet fired in to water, you know what water is Ted, that clear stuff before the booze, well never mind..

When drilling the ports I always went very slowly close to exit, also ground a drill with almost zero lip clearance, used the gas port in the cyl. with slipping fitting size drill fitting to start the port, this prevented drill drift..

It's time for the other Member named Art to use his last name letter, I was here first.. Is that to much for you Ted? Art

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Old August 23rd, 2016, 03:43 PM   #9
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I know who you are Art, but I'm not sure if I know the other Art. There is an art to all this nonsense... By the way, they don't have any of those Tex-Mex restaurants around here, but I did find a very good Mexican food place. They even serve a complimentary Tequila slammer after dinner. My treat if you ever can make it out to Oregon.

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Old August 24th, 2016, 03:49 AM   #10
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Gas port fully in the land or groove would seem "right". The groove is larger, so aim for that. However, barrel timing, headspace and torque etc would seem more important.

As for a gas port in the land snagging bullet material; "no". Sure, the land engraving pressure is very high at the throat. However, by the time the bullet reaches the gas port the contact pressure between bullet and barrel is no higher at the lands than at the grooves (unless bore diameter necks down significantly towards the muzzle).

As for a burr causing trouble; that can happen just as badly with the port in the groove. While a burr is undesirable, a small burr will get worn or "burnt off" pretty quickly; so do your serious evaluation after a few rounds.

While the gas port erosion shown 2/3 of the way down this page is extreme after thousands of rounds, it doesn't take much imagination to see that the "trailing edge" of the gas port will get rounded off first from hot gas and propellant particle "sand blasting": http://www.luckygunner.com/labs/bras...el-cased-ammo/

So; if the gas port does not snag on a patch the first time you wipe out the barrel before shooting, it probably won't shave any bullets either.

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Old August 24th, 2016, 04:09 AM   #11
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Another Art

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I know who you are Art, but I'm not sure if I know the other Art. There is an art to all this nonsense... By the way, they don't have any of those Tex-Mex restaurants around here, but I did find a very good Mexican food place. They even serve a complimentary Tequila slammer after dinner. My treat if you ever can make it out to Oregon.


I think the other Art is " Shooting Sights" ..

Would like to get up your way someday, spent two days at Ore. St. College, nice small Town, pretty Country, lots of free mud..

Found a new place close to Medina, that's over by Leaky,, all the Ribs you can eat for $5.99 on Wed.'s, sign on the door says "No shoes No shirt No Ribs".. Walk through twice and your booths are waterproof.

I reduced your 4895 charge to 39.5 in PMC cases and it is super consistent.

Can you rig your Barreling machine to remove as well?? Art

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Old August 24th, 2016, 04:19 AM   #12
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Shave the Bullets?

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Gas port fully in the land or groove would seem "right". The groove is larger, so aim for that. However, barrel timing, headspace and torque etc would seem more important.

As for a gas port in the land snagging bullet material; "no". Sure, the land engraving pressure is very high at the throat. However, by the time the bullet reaches the gas port the contact pressure between bullet and barrel is no higher at the lands than at the grooves (unless bore diameter necks down significantly towards the muzzle).

As for a burr causing trouble; that can happen just as badly with the port in the groove. While a burr is undesirable, a small burr will get worn or "burnt off" pretty quickly; so do your serious evaluation after a few rounds.

While the gas port erosion shown 2/3 of the way down this page is extreme after thousands of rounds, it doesn't take much imagination to see that the "trailing edge" of the gas port will get rounded off first from hot gas and propellant particle "sand blasting": http://www.luckygunner.com/labs/bras...el-cased-ammo/

So; if the gas port does not snag on a patch the first time you wipe out the barrel before shooting, it probably won't shave any bullets either.

I don't know if a snag will shave the bullet or not, a snagged patch only tells me there is something not wanted at the port.

I agree, a few rounds and whatever is there will be gone...Art

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Old August 24th, 2016, 04:22 AM   #13
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Art seems to be a popular name on the forum.
I have attempted to remember to use Semper Fi Art to differentiate.
Maybe I should just use ArtB. That works. Shooting sight Art would be ArtN.
Oh the confusion. Yep , you were here first Old Timer. He He.
ArtB

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Old August 24th, 2016, 09:42 AM   #14
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I hadn't thought of trying to use the barreling machine to remove the barrel. It was never intended to do that. I have a really big receiver wrench (made by Pat Patnaud, RIP) and one of the blocks used in the military barrel vise. I use the block in my bench vise to hold the BA while turning the receiver with the big wrench. Works great. My bench vise is older than I am by the way. I think disassembly could be done using the torque gage, but I don't much want to use such an expensive gage for that. I always prefer to use the proper tool for the job when possible.

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Old August 24th, 2016, 09:43 AM   #15
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A few things:

1) The grooves are usually wider that the lands, so there is more room for a port.

2) The bullet or bullet jacket material under the lands is under significantly more compression than that in the grooves. So, the shaving of jacket material is less likely. The worst case situation regarding shaving on jacket or rotating band material would be to have the port encroach on the discontinuity between a land and groove. Although, shaving of the bullet jacket is not extremely likely, it is certainly not optimal. It should be noted that large caliber small arms, 20mm to 35mm, with a large number of small width lands and grooves, the boring of a gas port that is entirely within a land or groove is virtually impossible, and these shells are often fitted with a soft or highly 'springy' rotating bands (nylon) which makes shaving more likely.

3) The gas port is going to erode, and the erosion pattern is well known, a long furrow immediately ahead of the gas port. If the gas port in centered in a land, given the relatively shallow angle is rifling, even high twists, it will allow the erosion path to stay clear of crossing the land/groove boundary, or at least a longer time before the erosion does cross.

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