For a Garand, for safety sake, you should always full length size your cases.
This is the Process I follow:
1. Set up your sizing dies with a cartridge headspace gage. Size to gage minimum.
2.Trim cases.
3. I recommend reaming primer pockets to depth.
4. Always seat all primers with a hand tool (I use the Lee) and inspect each and every primer to determine that it is below the case head.
I do not recommend Federal primers, they are extremely sensitive and gained a reputation for slamfires in M1’s and M1a’s. I use CCI #34’s for gas guns, they require a good wack to ignite.
4. Dump your favorite powder. For Garands, anything in the 4895 burn rate will do well.
So many people reload for bolt rifles that they are used to what would be sloppy reloading practices for auto rifles.
As long as the bolt cams engage, you can crush fit an oversized cartridge in a bolt gun. That is why neck sizing is so popular and hardly any bolt gunners ever set up their dies with a case gage. They just crush fit the ammo in the chamber and can't even feel it when they are doing it.
Gas guns will jam with ammo that will chamber in bolt rifles.
Garands and M1'a do have the inertia to chamber slightly fat and slightly long cases. But it is a bad idea as bolt closure is delayed as the cartridge is crush fit to the chamber. In that time period, that free floating firing is just tapping the heck out of the primer, and your lugs are not engaged.
That has, and will lead, to out of battery slamfires.
Most of my gas guns are match rifles. I have a few rifles with military chambers. Chambers in military rifles are huge. The cases come out huge too.
Regardless of the type of sizing die, for rifles you should always use a cartridge headspace gage to set up your sizing die.
You simply size the case, drop it in the gage, and see if it is between the Go and No Go ledges.
Wilson gage with new Winchester brass.
I own a number of Wilson cartridge headspace gages. They cost about $25.00. These work great in setting up your dies to size the case to SAAMI lengths. These gages are also oversize between the shoulder and the base, so you can drop a fired case in the gage and roughly measure the headspace of your rifle.
But a Wilson gage won't tell you if the sized round is too fat.
I also have reamer cut gages. I have asked the gunsmiths who chamber my match rifles to use their chambering reamers and cut me a dimensionally correct chamber from a barrel stub. I can use this gage to tell me if my ammunition is too fat as well as being too long.
I now can gage brass in a "duplicate" chamber. This has lead me to the use of small base dies. As an example, I found two huge fired WRA 68 cases. One would drop all the way in the Wilson gage, but the other would not drop in the reamer cut gage.
After sizing with a standard Lee sizing die, one case would not drop all the way in the reamer cut gage. After sizing with a Redding small base die, the other case would drop in the reamer cut gage.
If you want to improve your feed and extraction reliability in a semi auto, you should use small base dies.
A couple of caveats, one is that you must set up a small base die with a cartridge headspace gage or you will set the case shoulder back too much. This is the origin of those myths that state small base dies oversize brass. They will if you don’t gage your die set up.
The second caveat is that spray on lubes don’t have the lubricity necessary to small base size. You will turn your bench over trying to small base size if all you are using is a spray on lube. Imperial sizing wax and RCBS water soluble work just fine in small base dies.
Once fired WRA 68, one drops in Wilson gage, the other won’t drop in reamer cut gage.
WRA 68 case sized in Lee sizing die, won't drop in reamer cut gage
WRA68 case sized in Redding small base die, drops in reamer cut gage
