Originally Posted by TLuker
There's a lot that goes into dialing in a gun. Finding the bullet it likes is part of it. A lot of the mil-surplus is 62gr and it was made for a barrel with a 1:7 rate of twist. The mini is 1:9. It will shoot the mil-surplus stuff but accuracy at distance can suffer. Mine doen't like 62 gr bullets. I just don't think there is enough spin in the 1:9 barrel of the mini to stabilize a 62 gr bullet. On the flip size a lot of the lighter bullets made for varmints can fly apart because they were built for the 1:12 rate of twist in most varmint rifles. Try different bullets until you find one it likes and try those bullets at longer distances.
M855/SS109 is known to have poor accuracy. The mil-spec for M855 calls for 95% to hit an 8x8 inch square at 200yds through a test barrel, that's worse than 4MOA. Current production I've heard is worse, since the DOD been granting exemptions on meeting specs, in order to meet demand. The problem with M855 is the steel perpetrator is almost never centered perfectly, resulting in an unbalanced bullet.
On twist, a 1 in 9 should handle anything from 40-73gr, some might handle heavier 75-77gr, but not likely. Longer barrels can handle heavier bullets than short barrels, since the increased muzzle velocity means the bullet is spinning faster.