My advice for reloading for Garands/M1a’s is to
1. Full length resize in a small base die
2. Trim cases
3. Clean primer pockets, ream to depth
4. Prime all cases by hand, verify that all primers are below the case head, and use the least sensitive primers you can find.
5. Use IMR4895/AA2495/H4895 powders.
6. Seat the bullets to magazine depth, no longer than 3.3” inches for the 30-06, no longer than 2.8 for the 308, shorter is fine.
The Garand has a free floating firing pin, like this M1 carbine. The M1 Carbine and the M1 Garand have a firing pin retraction cam. This cam pulls the firing pin back during extraction. It also has limited utility as a safety device, but is easily defeated by tight or long rounds. If you sized your round smaller than the chamber the odds would will be in your favor to have an in battery slamfire.
Only at final cam down is the firing pin retracted. Up to then the firing pin is totally free floating and tapping the heck out of the primer.
This is a M1 Carbine firing pin retraction cam.
This is the M1 Garand firing pin retraction cam they are functionally identical, just the carbine is easier to visually understand.
This is a M1 Garand receiver and the firing pin is fully forward and just touching the firing pin retraction cam. As you can see there is only thousand's of an inch of forward movement left in bolt cam down and yet the firing pin is out about 0.064" of the bolt face.
This is the location where out of battery slamfires occur.
If the bolt has to stop here to crunch fit a long case or a fat case that firing pin is rebounding off the back of the primer at its highest velocity and the lugs are not engaged.
That is why it is important to small base size cases used in these rifles and to set up the dies with a case gage and size to gage minimum. (Assuming you don’t know the headspace of your chamber, if you do, always be 0.002 to 0.003” less) You want the bolt to close without resistance. This will reduce the risk of an out of battery slamfire.
There are some who say small base dies are not needed in these rifles, the Gunwriter Mike Venturino has been one. For years he has been saying in print that only standard sizing dies are need. But in the July 2012 issue of Guns Magazine, he is testing an M1a and a AR10 and his reloads are too tight. I find it humorous to read of him beating the bolts open with scrap lumber. Ha, Ha.
If you attempt to small base size with a spray on lube you will stick the case in the die. I recommend RCBS water soluble or Imperial Sizing wax. These are excellent lubes.
For these rifles it is safety critical to ensure ream primer pockets are at depth, reaming them to depth is a good idea, seat the primers by hand, and verify that all of the primers are below the primer pocket. There is a chance that a cocked primer, with the anvil firmly seated on something, will cause a primer initiated slamfire. One poster swaged his primer pockets, which shaved brass donuts into the pocket. He left the donuts in the pocket, which resulted in high primers, and his AR10 slamfired in battery. Clean those pockets! A high primer can cause a slamfire but only if the anvil is firmly seated. High primers are one of the most common cause of misfires because the primer won't fire unless the anvil is seated and is pushed up into the primer cake.
http://www.shootingtimes.com/2011/01/04/ammunition_st_mamotaip_200909/ However, given a shallow pocket it is theoretically possible that high primers could slamfire, given debris in the pocket, you can get a slamfire.
Mr Faatz stuffed an extra anvil in his primers pocket as he was unable to get unsupported high primers to ignite. Reference A.
Just examine the back of the ammunition you have and see if there are high or cocked primers.
It is also safety critical to use the least sensitive primer around because these rifles will slamfire in battery or worse, out of battery, given a sensitive enough primer.
Federal primers are the most sensitive primer on the market and the most "slamfiring" primer in Garands. I have lots of web accounts of slamfires with Federal primers. Don’t use them. I recommend CCI #34's and Tula7.62 primers as they considered "Mil Spec" primers. Which means they are less sensitive than commercial primers, federal being the most sensitive commercial primer on the market. Rifles do slamfire with “mil spec” primers, it is just the frequency is far less. I have accounts of slamfires in AK47’s, FAL’s, FN 49, SKS’s, AR15’s, AR10’s, MAS 49/56, M1 carbines, Tokerev SVT , commercial BAR, and probably more types which I did not keep a record. More slamfire accounts with Garands are currently being posted than any other type probably due to the high number acquired from the CMP and the long, heavy firing pin of the Garand.
The only mechanism which I have not found a true “primer initiated” slamfire is the HK91 mechanisms. And that is probably due to the incredibly stiff firing spring to be found in roller bolts.
When firing single shot, use a SLED. Do not put a round in the chamber and drop the bolt. Lots of inbattery slamfires, and a few out of battery, have happened because of this. You want to slow the bolt down. When rounds feed from the clip the friction between cartridges slows the bolt a bit. You want to use a SLED as that slows the bolt a bit.
If loading a Garand without a SLED, lower the bolt about 1” over the follower and let go. Always get your hand out of the way so that if the mechanism slamfires the operating rod does not cut through the palm of your hand.
This guy said he had been shooting M1a’s for 15 years and never had a slamfire. He put a tight case in the chamber, it had a CCI #34 primer, and dropped the bolt.
His chances of an inbattery slamfire would have been much better without an interference fit case.
Use powders that are close to IMR 4895 in burning rate or just use IMR 4895. High port pressures are the concern. High pressures will create excessive operating rod acceleration. Reference b. recommends choosing powders that have burning rates between IMR3031 and IMR4320. This includes powders such as IMR 4064, and Winchester 748. Accurate Arms stated that AA2520, AA2495 and 2700 are their best powders for the M1 Garands. Some have noticed that AA2700 is actually a slow burning powder, listed as even slower than IMR 4350. But Accurate Arms told me, that because it is a ball powder, the pressure curve has dropped enough that port pressures are not excessive for a Garand. I believe the first choice of powders are IMR 4985, H4895, AA2495. In the 30-06 I have used a load of 168 grain Sierra Match, 47.0 grains IMR4895, LC cases, and CCI #34 primers OAL 3.300” for years. This is a great target load, should be considered a maximum load, does not hurt a thing to cut it a grain or two, and it shoots great in my match Garands.
Tried the Tula 7.62 primers this year and they shoot well:
Other targets with the CCI #34 primer:
Check cartridges for case head separation. Gas guns are hard on brass: the bolt unlocks while there is still significant chamber pressure. Because of this the case gets stretched on extraction. Carefully inspect cases for stretch ring marks. They occur about .4” of an inch ahead of the base. You can verify if the cases are internally necking by inserting a bent paperclip in the case, and feeling for an edge. A number of shooters I have asked claim various case lives in the M1 or M1A. Some have case head separations about the fifth reload, like the ones from a bud’s M1a below. Others have taken their cases up to ten reloads. The useful lifetime of a case is determined by case head separations, case neck splitting, or primer pocket enlargement. When any one of these failure mechanisms happens to a case, it has exceeded its operational lifetime. In my experience, US military brass holds up better than commercial cases. But this is a broad generalization. You want to use heavy cases over light cases.
References:
a. The Mysterious Slam-Fire, American Rifleman, Oct 1983
b. Reloading for the M1 Rifle, American Rifleman, Mar 1986
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