I bought a M1S upper and then later found out about SPCI and II barrels. I called M1S and was told that it is marked 1-9.5 but it really is a 1-10 twist. I verified that with my own twist rate check and it is a 1-10. I have the SPCI so I can't shoot the SSA Tac. loads = too much pressure. The 1-11 twist is for less than 100 gr hot loads from what I can understand about the suject. Hope this helps. You can also go to 68forums and get really good info from those guys.
Last edited by jhog; 01-19-2011 at 04:06 PM.
Reason: added a comment