What size bullets

[340six]

I have a real nice Garand CMP but is a very mint one. All #'s match and late 5-
Just shot a few with 35 Grains Varget at 308"
Shot .308" Jacketed, and .309" 311365's As well as gave some to others to test at CMP Board and they shot .309" well out guns with good barrels.
I now have a 1903-A4 clone with a barrel that just has a few hundred out it
Never slugged the barrels never shot it yet.
And built a new AR in 300Blk so want to try then in it with 11 grains of 1680
I was gonna go with .309" again but ran across a .311" in my stuff I never knew I had.
Should I go with whats works? And not fix what is not broken?

[ShooterAZ]

I size .310 or .311 for all of my 30 Caliber rifles except for the 30 Carbine which gets sized to .309. 309 obviously works, but you "may" get better accuracy by sizing a thou or two larger.

[Jack Stanley]

If it's a military barrel you probably won't have a problem with the larger bullet . A commercial barrel might be a bit tighter in the neck and throat area .

Jack

[vernm]

After slugging the chamber free bore (ball seat) on my 1903 and 1903A3 rifles and making sure larger sized bullets would chamber freely, I size bullets for these rifles at .312. They shoot well and don't lead. The diameter of the neck of a loaded round with a .312 cast bullet is a couple thousandths smaller than the neck of a fired case in my rifles. I found that it is important to have sufficient room for the neck to expand and release the bullet after opening the primer pockets of some expensive brass. The 300 BO is a different story. Some 223Rem cases are too thick in the area just behind the shoulder which becomes the neck of the 300 BO case. With the thinnest case (Winchester Commercial) I could not use a cast bullet larger than .309. Rounds loaded with larger bullets measured larger in the neck than a fired case. Also, any semiauto firearm needs a little "wiggle" room in the chamber to feed reliably.

[Moonie]

I size .310 for all my 30 calibers.