NEVER TRIM more than 4x.....

[memilanuk]

Typically because gas-operated guns are a tad sensitive to port pressure and timing. Depending on how they're set up, the bolt may be starting to unlock while there is still considerable pressure in the chamber. Even if thats not the case (no pun intended) the extraction process often starts before the brass casing has had time to fully shrink back down and release its hold on the chamber walls. With the bolt unlocking and moving back, and the case still gripping the chamber walls... stretching is inevitable.

 

[jlow]

Typically because gas-operated guns are a tad sensitive to port pressure and timing. Depending on how they're set up, the bolt may be starting to unlock while there is still considerable pressure in the chamber. Even if thats not the case (no pun intended) the extraction process often starts before the brass casing has had time to fully shrink back down and release its hold on the chamber walls. With the bolt unlocking and moving back, and the case still gripping the chamber walls... stretching is inevitable.

Understand the problem with extraction with the gas gun. I have a number of gas guns including an OBR in 7.62 and it is hard on the brass for the reasons you mentioned. However, my problem is with rim bending and not body thinning. I also do think that can it be minimized with an adjustable gas block, but that is BESIDE the point of the current question.

So going back again. I am told that an M1A can have over 50 thousands neck growth over five firing and that cause case thinning which can result in case head separation.

So assuming worst case extraction which is stretch the case body, how does that relate to the neck growing 50 thousands? Stretching due to premature extraction seems like is different than neck growth causing body thinning.

 

[memilanuk]

Where do you think that 50 thou of brass is coming from? The body stretches, then we size the body. The shoulder may get bumped back, but the material doesn't get put back where it was - it extruded out the top of the die, ie the neck.

 

[riflewoman]

One of the reasons for case growth in gas guns is how they’re chambered and how the ammo for them is reloaded (resized).

When I rebarreled a gas gun, I cut my chambers to headspace at “GO plus .002”. Then I sized the brass to the low end on the Wilson case gauge. The reason was for reliable functioning AND to prevent SLAMFIRES. if the chamber clearances get too tight, an M1A can slamfire. If the clearances get minimal functioning can get sluggish causing alibis.

The case life suffers but that is just a trade off you just have to live with.

 

[Uncle Ed]

On M1/M1A type rifles the resized case should be .003 to .005 smaller in diameter than its fired diameter. This allows the case to spring back from the chamber walls and extract reliably. Reducing the fired case diameter during sizing increases case growth and the need to trim.

H a n d l o a d i n g f o r C o m p e t i t i o n
G l e n D . Z e d i k e r
SECTION 9
RELOADING FOR THE MATCH M14
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=2ahUKEwjbmZrh-aTfAhVQmlkKHZtQA7sQFjAMegQIDBAC&url=http://www.zediker.com/downloads/14_loading.pdf&usg=AOvVaw0tVzg215hdzh0mGPudTRx0

 

[jlow]

OK, that sloppy intentional chamber clearance idea to avoid slamfire make good sense - thanks. That likely is the answer I was looking for.

I was puzzled because my AR-10 gas gun never has any of these problems but that is likely because it has a spring on the primer pin and that explains why they can go much tighter tolerance without any slamfire problem and the brass last much longer and do not have the huge neck growth or case head separation....

 

[Brians356]

I eventually came to the conclusion that the Lee bolt construction and locking arrangements allowed the bolt to twist in one direction under firing pressure and that in a box of 50 cases being loaded multiple times, random positioning in the chamber would see extremes of one or two cases positioned with the same side at any given point of the chamber / bolt-face on every or nearly every firing causing whichever section of case wall that stretched more to be rapidly weakened whilst at the other extreme one or two cases got a different position each time spreading the stretching out over more case wall and giving better life. Most were in between the extremes.

Then by indexing cases with ink, all you had to do was rotate each case in this order: 0, 180, 90, 270 degrees, reiterate. Rather like tightening four lug nuts on a wheel. You might then get double or treble the useful life out of them, hey?
-

 

[Laurie]

That would have been an interesting experiment, also to see if it affected groups. (Creighton Audette discovered through such experiments many years back that poorly drawn brass that had walls more than 0.003" thicker on one side than the other flexed in the chamber and produced a flier. By marking and indexing cases, he was able to predict the direction the flier would take, also that putting the thick side to the same position in the chamber for each shot would produce smaller groups. The still in production NECO concentricity gauge is a copy of an Audette design he worked up to measure case wall thickness from the inside to check and batch cases for this purpose. Logically, if a 'banana case' affects groups, so might brass in Lee-Enfields that has stretched more on one side than the other .......... ??)

In the days when I shot a 7.62 Enfield, if it went bang reliably and shot within 2-MOA with iron sights, I was happy .......... a time when life was simpler but arguably duller. There is a reason though why the first generation Lee based 7.62 TR rifles were soon overtaken by the multi-lug SWING and Barnard actions and you can hardly give them away these days in the UK when in this form. (They still work well with 223 though, and I believe a fair few remain in service in Canadian TR circles in this guise.)

 

[6MMsteve]

I shoot a custom chambered .308 and trim minimal brass every firing. I have brass with 13 firings on it and we have cut one open to brass thickness. The primer pockets will be loose before the brass gets thin.

a bore scope comes in handy sometimes to chk the thinning I use my lyman borescope just slide it in the neck and you see.... I don't shoot that much but I was just wondering one day that's all, but it does show the thinning

 

[Jennb]

Do what you want but I full length size with minimal bump and trim every time. These have been fired 13 times and I continue to use the brass. Primer pockets will go first.

 

[mike a]

View attachment 1080510 Do what you want but I full length size with minimal bump and trim every time. These have been fired 13 times and I continue to use the brass. Primer pockets will go first.

I will do what I want and stop here. 6.5 creed 15x, trimmed I don't know how much. You can clearly see the thinning. This thread got me curious and your pics inspired me to check. Glad I did.

 

[Jennb]

I will do what I want and stop here. 6.5 creed 15x, trimmed I don't know how much. You can clearly see the thinning. This thread got me curious and your pics inspired me to check. Glad I did.

Now you know.

 

[Idaho-Lefty]

@ Uncle Ed,.. Thanks again, for your insight on, Bullet "run-out" and "best" Dies, to buy ! I have 2 sets of, Forster FL dies coming and I will ship them off soon, to open up the Necks, for .0025-.003 "Tension" on the Bullet and so, I'm NOT "over working", the Brass ! My Rifles are primarily Hunting Rifles first, Target shooting, 2nd use. I believe in FL sizing with, minimal shoulder "bump" to avoid stretching and NOW I won't be ruining/ overworking, the "Neck's" thanks, to your Info !
ALSO thanks, for posting the Chart on, Brass reload-ability, PROVING what I've believed all along, that,.. REMINGTON Brass, is some "pretty good, chit" ! I use it in my .270 WSM, .22-250 Rem. and .243 Win. I have some, OLD Winchester .22-250 Brass that, is pretty good, too ! SADLY Winchester, is NOW making,.. "KRAPPY" Brass ! ! Thanks again, for your help !