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Reloaders - 7.62/308 Shoulder Expansion Info.

6K views 35 replies 11 participants last post by  Ole Silver 
#1 ·
I Wish All a Happy & Safe Memorial Day Weekend.

I would like to know what you all are seeing as far as shoulder push/expansion on your fired cases.

I have a RCBS Mic that I trust as it verifies against a known chamber and my Hornady tools as well.

I am seeing an average shoulder push of about .015 on my fired brass. It is pretty dog gone consistant.

What are you guys seeing on your fired cases?

My 308 bolt gun is dead nuts on at 1.630. Fire formed cases come in at 1.628 - 1.629 with most being 1.629. That's how I know that my RCBS mic is dead on.

I guess a .015 push on the shoulder is why these M1A/M14 rifles are tough on brass. I pretty much have assumed that and I am annealing the brass.

Looking forward to hearing from you all.

Happy Weekend to All of My Brothers out there.

Ole Silver
 
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#30 ·
Size your cases to around 0.004" under your rifle chamber headspace and you should be good. After firing your brass should come out all roughly the same cartridge headspace length. I found that measuring before and after firing and comparing the two cleared up a lot of mystery about headspace. The wild card in the M1A / M14 world is the effect of the forcefull ejection on the case, every rifle is different and will subject each ejected case to it's own version of torture.

John
 
#31 ·
Greatplainsrifleman & Vanagonjon,

Thank you both for your responses.

My chamber is cut at 1.6315 dead nuts on my M1A. I resize my cases to 1.628-1.629. I know the chamber HS is right as I use my RCBS mic to validate my measurements when I gut the bolt and test the brass for bolt closure. The bolt will close on 1.631 & I would have to muscle it to close on 1.632. The RCBS mic validates that the HS hang tag of 1.6315 from SAI is OK.

I do no do any fireforming work on the M1A cases. Simple reason is that they won't fit into a case gauge after firing. I full length resize. I fired 200 rounds today of my reloads. GGG brass, 168 Nosler custom comps, CCI#34 primers, 41.5 of IMR4064, brass sized at 1.628-1.629, COAL 2.820. I checked when I got home & the fired brass was between 1.642 & 1.645. The rifle functioned without flaw.

I guess that is just the nature of the Beast.

In short, I only fireform for my bolt guns.

I have a screwed/staked unitized gas system on the M1A so I can't just turn it off to test that way.

Thanks for Your Feedback Guys!!!!!!!

Ole Silver
 
#32 ·
I'll bet that your throat is long. The only way to know for sure is by casting the chamber using Cerrosafe. I've done that to my SOCOM and it has a long throat and the brass from my SOCOM is always stretched more than the brass from my Loaded model rifle. The Loaded model has a far tighter chamber in both diameter and length specs.

An alternative way of checking the throat would be to measure the length of the case's neck before and after firing. If the neck stretch causes most of the total case stretch then I'd say that the throat is long.

According to SAAMI specs the neck should be about 0.321" long as measured from the shoulder to the mouth.
 
#33 · (Edited)
RAMMAC,

I think you are correct.

I fired 200 reloads done with GGG brass a couple of days ago testing my magazines. Brass was once fired from LEO bolt rifles. Straight & clean.

65% of my reloads were less than .001 runout on a NECO guage. 30% were .002 or less & the last 5% were 3% or less.

I did my usual prep on the cases. Deprime, uniform primer pockets, tumble, size the case body with a Redding die. No neck sizing, just case body & shoulder push back to 1.628-9. Resized the necks with a Forster bushing neck sizer.

I reloaded the same cases and got 30% .001 or less runout 60% .002 or less runout and nothing else over .003.

That was puzzling to me. I was paying real close attention to all the details as I really like the GGG brass.

Here is the kicker. The brass, after tumbling, did not clean up as well on one side of the necks. The dirty side was the low side when I ran the loaded rounds on the NECO for runout.

I think I may have a messy chamber. 1968 SAK USGI Chrome lined 22 inch. Chamber cleaned religiously.

What do you think?

Thanks RAMMAC,

Ole Silver
 
#34 ·
41.5gr of IMR 4064 sure doesn't seem like a hot load that would wear the chamber a lot. I think either the chamber was cut a little out of spec of there has been a lot of rounds through it.

There is one other possibility; there could be excess movement of the bolt due to either the receiver being out of spec or the bolt lugs being worn.
 
#35 ·
RAMMAC,

I bought this 1990 SAI syandard abotu 2 & 1/2 years ago. It didn't look like it had hardly been fired. The owner said he couldn't get it to shoot straight.

I had a smith look at the barrel and he said it looked almost virgin. My wife was almost virgin too when I met her.

I downranged a few hundred rounds of junk, semi junk, good milsurp & good ammo. American Eagle & FGMM.

It stunk bad with everything but the American Eagle. It still wasn't that good & then the FGMM was not all that impressive either.

That's when I decided to make some mods.

First was fitting the handguard so that the action wasn't filing wood.
Second was shimming the GS.
Third was installing a Sadlak op rod spring guide & Tubbs spring.
Fourth was a WIN trigger group from Elmer.
Fifth was ream GI flash suppressor.
Sixth was a unitzed GS from Hueygunner / Tried Sadlak piston. Rifle didn't like it.
Seventh was adjusting dwell time.
Eigth was a JAE Gen2 Stock & Leupold Scope/Bassett mount.

I almost forgot - I realligned the oprod guide.
Also, Put a dab of high temp silicon under the handguard.

Relieving the handguard & shimming the gas system had the biggest effect with the exception of the JAE stock. That made a huge difference immediately.

It shoots very well now. Some of my handloads are grouping under an inch rapid fire at 100 meters with my handloads.

I put the rifle back into a proven good USGI fiberglass stock. Really tight fit and strong lockup. That's what I have been testing with while Jon Wolfe finishes my M25 build.

It's just a 1990 SAI standard that I can depend on and just as loose as some of my old girlfreinds. Still dependable too!!!!!!

As a reloader I am just trying to figure out why it is tweaking my brass.

Verbose I know. Too much iced tea today.

Ole Silver
 
#36 ·
Got the Jon Wolfe M25 and here is what I've observed.

The chamber on the WMMW barrel is cut in such a way that Nosler 168CC's touch the lands at a COAL of 2.820. That said, I had to push the pills deeper on my reloads as they were loaded for my old stretched out SAK barrel.

Went to the range today & tested the new rifle. It functioned flawlessly. I was ready to run 100 rounds through it but stopped after 70. I went through the cleaning routine for the new barrel and just had a blast.

My GGG brass with Nosler 168CC's in front of 41.5 of IMR4064 gave me consistent 1.5 inch groups. Some of the other loads didn't do quite as well. I was firing 10 shot groups rapid and felt like a kid again.

When I got home I measured the shoulder push on the brass and it was between .003 & .004 on everything.

I guess my old SAK barrel is either not cut right or it is just plain shot out.

I am talking to Jon Wolfe about a 18.5 WMMW fluted barrel and just need to get the wife to agree that would be a good Christmas present for me & my old SA standard. I was thinking about a M1 tanker but the old SA with a shorter barrel will make a real nice scout/field rifle. I will more than likely be buried with it.

Jon Wolfe built me an outstanding rifle.

Ole Silver
 
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