[Ted Brown]

I assume you are talking about the M14 rifle.
It really doesn't matter all that much which twist you use between 1:10", 1:11", or 1:12". I have stuck with 1:10" in most of my persoanl rifles.
You will get the best overall accuracy with a 22" barrel, but some 18.5" barrels shoot pretty good too.
As for bullets, not all rifles perform their best with the same bullets, but they usually shoot best with match grade bullets like Sierra Match Kings, Hornady Match or A-Max, or Nosler Match. Stay with bullets in the 150 to 175 grain range. Most rifles really like the 168 grain bullets out to 600 yards. 175 grain will shoot well out to 1000 yards. Some rifles will even shoot well with the 180 grain SMK at long range.

 

[cfl18]

Yes I was talking about m14 I have have tried 150 and 168 and my 18.5 scout 1 in 11 twist barrel likes the 150 over the 168 it shoots much tighter groups. The 150 were non match. The 168 are on papper but all over the place in about a 8" circle. The 150 non match were about 2.5"-3" @ 100 yards