I loaded 168 gr hornady match hpbt with imr 4895 41.5 (weighed individually)grains for my m1a. coal was 2.80-2.790 . brass was lake city but there may have been pmc. I chronoed it at 2573 fps . looked at the brass and no signs of high pressure.
I experienced failure to extract with 2-3 cartridges. the m1a didn't cycle. the 1st that I pulled the bolt back on may have been sticky but I think it was me trying to figure out why my gun wasn't firing the subsequent shot but the other 2 times knowing what to expect it did not seem sticky maybe not as easy as pulling an empty bolt back.
Did you full length resize your brass, and did you use a small base die?
For these rifles, you should always full length size, you should set up your sizing die with a case gage, size to gage minimum, and it is best practice to use small base dies.
The case must enter the chamber without any resistance to bolt closure. The case must be smaller than the chamber, ideally the shoulder should be 0.003” less than the chamber, and the case diameter should be such, that upon extraction, it is off the chamber walls as the case moves out. If the case starts out “fat”, it will be clinging to the chamber walls on extraction, and you will experience failures to extract.
Cases fired in another chamber are likely to be too large, even after sizing with a standard based die. Small base dies may reduce a large case enough to be safe in a M1a. But sometimes, even a small base die can’t reduce a ballooned case enough. I have 308 and 30-6 gages, cut by Gene Barnett which are a little out of the ordinary. He cut these gages with his chambering reamer. Standard cartridge headspace gages are cut with a special reamer that is wide in the middle. A standard cartridge headspace gage measures length, not “fatness”. A reamer cut headspace gage will show you if the case is too long and too “fat” for that chamber.
I have a number of 308 small base dies, and I still have my Lee standard die.
I sized a number of my match cases in the Lee die. All of them dropped in the reamer cut case gage. So, if you said you don’t need small base dies, you would be correct most of the time.
So now I had to scratch around trying to find cases that would prove my point.
These two cases are once fired range pickup brass that I found in my brass box. I had to go through about 20 cases before I found a set of really ballooned cases. On the right is the Barnett reamer cut gage.
If you notice one case has completed dropped into the Wilson cartridge headspace gage, while the other has not dropped into the Barnett reamer cut gage. This shows how much they have swelled up after being fired. Must have been a big chamber.
The second picture is of the fattest of the group after sizing in with Lee Die. I trimmed the thing to make sure that the case neck did not interfere with the throat in the gage.
Hopefully you can see that the case did not drop all the way in the case gage. At least on its own. It would have taken a good hard push to get that base all the way in.
This is after resizing in my RCBS small base die. I could not find the RCBS box, so the case/gage are sitting on a Redding small base box. However, that little additional sizing removed the interference fit.
Sometimes cases are so ballooned that even a small base die won’t reduce the case to factory dimensions. It all depends on the chamber the round was fired in.
I know it is extra effort to size cases with small base dies, if you use a good lube like Imperial Sizing wax or RCBS case lube, the effort is somewhat reduced. Still for all the extra bother involved in sizing with small base dies I'll do it for my Garands and M1a's. With those rifles I don’t want any resistance to chambering, I don’t want any delay to bolt closure. Because as the bolt stops and the lugs are turning, that darn free floating firing pin is just tapping the heck out of the primer.
