My advice:
Set up your sizing dies with a Wilson type cartridge headspace gage. Size to gage minimum. You do not want any delay to bolt closure due to over long cases. This and primer sensitivity are very, very, important safety considerations.
I small base size. This is a risk reduction effort. You do not want overlong or too fat of cases for your 308 M1a. Anything that delays bolt closure only increase the chance of an out of battery slamfire. The only case lubes that work well with my small base dies are RCBS case lube or Imperial Wax. Everything else requires too much effort. .
Trim your cases to 2.000” (or less, but two inches is easy to remember) after sizing. I always trim my cases between each firing, but I have a Giraud trimmer.
http://www.giraudtool.com/ With this trimmer it takes less time to trim than to measure the cases.
I highly recommend reaming your pockets to depth. Prime your brass with a hand held tool and always check to see that the primer is below the case head. No high primers! This is a safety issue in semi auto’s.
I recommend CCI #34 primers. They are the least sensitive primers out there. You do not want to use any primer that is “more sensitive”. Do not use Federals. When friends have discussed their slamfires, and mine (!) federals were the primers involved in all of our slamfires in M1 Garands or M1a’s.
The M14 was designed with IMR 4895 as the propellant. I recommend IMR 4895, AA2495, or H4895. These powders shoot exceptionally well and give appropriate port pressures. If you have to have a ball powder, AA2520 used to be very popular with M1a match shooters.
I seat all bullets to less than 2.800”. Currently I am seating all my 168’s to LT. 2.750”. I did load up some 150 FMJ’s, and they shot well at 2.75”. Bullets vary in length, so make sure none are longer than 2.800” or you will have troubles getting some in the magazine.
My match ammo, out to 300 yards is a 168 SMK/Nosler/Hornady Match, 41.0 grains IMR 4895/AA2494/H4895 LC cases CCI#34. OAL LT 2.800"
At long range I will bump up the charge to 41.5 grains with a 168.
Maybe some super duper shooter can tell the difference on target between a Sierra Match king, a Nosler Match, or a Hornady match, but in my hands and my rifles, they all shoot very well. I buy what is cheapest.
For 150 grain bullets, keep your velocities just at 2700 fps. Do not try to load bullets to 2800 or 2900 fps. That will be too hot for your M1a. For 168 Match bullets, I like to be between 2550 and 2625 fps. For 174 SMK around 2550 fps is fine, I don’t go over 2600 fps.
I found that 43-43.5 grains AA2520 with a 150 Hornady FMJ to give good accuracy and acceptable velocities.
For 168 SMK , the standard match load was somewhere between 40.5 grains IMR 4895 and 41.5 grains IMR 4895. I am using 41.0 IMR 4895 out to 300 yards. If I am using the 168 at 600 yards, I will bump it up to 41.5 grains.