Case Sizing In The M1a (and Garand)
Qasi, you raise a very important point, and one which I don't believe was really addressed in the course of this trek with the M1A.
I believe it is CRITICALLY important in M1/M1A rifles from the safety standpoint, that all cases are full-length sized. All other concerns (such as accuracy) are decidedly secondary to the proper sizing of brass for these rifles.
The reason lies in the design of the firing mechanisms. The firing pins in both rifles are of free-floating design, meaning they are unrestrained by springs or any other mechanical means. A glance at a round which has been chambered semi-automatically, but NOT fired, will show a dimple in the unfired primer. The dimple is caused by the firing pin exerting its inertia on the primer after forward motion of the bolt has ended.
Failure of partly-resized cases to chamber FREELY can lead to firing pin impacts with the case partly OUTSIDE the chamber and with the bolt unlocked. There have been enough partly-open-bolt slamfires in the rifle type to warrant serious concern in this matter. They are generally disastrous.
One more safety concern: due to the above condition of the firing pin impacting the primers, single loading can INCREASE the risk. If a single round is chambered by hand, and then the bolt is allowed to slam forward from its rear-most locked-open position, the bolt is traveling FASTER than it does in semi-auto firing. The effort expended in stripping a round from magazine or clip slows the bolt's speed considerably, and thus decreases the force of the firing pin's impact on the primer. SO, when single-loading an M1/M1A, allow the bolt to move forward under hand control to about half-way along its travel, and then release it. There will still be ample energy to lock the action closed on the round, and the possibility of a slam-fire is greatly reduced.
My primers for M1A/M1 are CCI#34, a magnum-strength 'military' primer. I have no plans to change. However, I used standard CCI#200s in my M1s, M1As, and M-14s in Canada for years, without difficulty. I would NOT consider using any pistol primer in these rifles, preferring to remain on the safe side.
So, to your question about my sizing routine: My "normal" routine right now calls for full-length sizing in an RCBS small-base .308 die. However, loading under some time pressure before the Nevada Cast Bullet Shoot last month, I managed to tear the rim off a case in my small-base die. Due to lack of time, I simply substituted my standard .308 sizer (non-small-base) and continued the run. No problems resulted, which was expected since I'd loaded thousands of rounds for earlier M-14s in Canada with the same die. Do I recommend the small-base die? YES, just for a bit more certainty and peace of mind.
A change is in the works, though. I now have an RCBS X-die (available in small-base configuration), which limits case-length growth to a very large degree. (Search for Larry Gibson's wonderful discussion of this die for M1A ammo.) The use of the X-die has been delayed while I rebuild the vertical column of my Unimat, to get enough clearance for an also-new Forster drill-press-mounted case trimmer. I want NOTHING to do with hand-trimming a thousand 7.62 cases!
Yep, my brass WAS unfired LC 7.62 NATO from GI Brass, but it sure's heck isn't "unfired" now! Cast-bullet pressures are apparently so low and so easy on the brass, that I have yet to discard even ONE case due to "wearing it out".
I use an L.E. Wilson .308 case gauge to check every single loaded round. I view this as an essential safety check for any semi-auto ammo I load, in any caliber. If a round fails to "chamber" easily in the gauge, I FIND OUT WHY....usually it's just a burr on the case rim from ejection or extraction, and the burr is easily removed with a needle file. However, if the round still doesn't enter the gauge freely, I turf it. No messing around, just get rid of it.
The gauge offers an easy way both to set the sizing die (size until the case seats flush with the rear face of the gauge) and also to check case length, because ANY protrusion of the case mouth beyond the front of the gauge indicates an over-length case. I have not had that problem yet, with at least three or four firings of all my brass with cast-bullet loads.
GET THE GAUGE, AND USE IT RELIGIOUSLY!!!!! It's about the best $20 we can spend, for insurance and confidence value.
I trust this answers your questions. Thanks for raising the subject, because it needed some airing.