Bought two M-40 Commemoratives in 2006 from Iron Brigade, SSA02## & SSA01##. Had IBA perform a complete accuracy suite on both weapons prior to shipping (Barrels pulled, Actions trued, Chambers re-cut to 1.630" exact, pillar bedding, triggers tuned and set to 3 3/4 lb-f, etc). Sourced and mounted a new 2nd Generation 3x9 Accu-Range Scope with '66 vintage 4 screw rings and Redfield Jr base on each. Both shoot "lights out" if I do my part with appropriate ammunition.
Just borescoped one and measured the twist at 1 turn in 12. End Flaps on both rifle's carton & Instruction Books are stamped 24" VAR Bbl. Reviewed my e-mail string with IBA when I bought and accurized these weapons and confirmed bbl contour and twist specs. I recall being a bit surprised at the 1 in 12 at the time based on what I had read in the literature (Senich, et al), but IBA maintained that the twist on the original M-40 were 1 in 12 as opposed to 1 in 10.
My personal experience with both weapons is that they love 168's (Old Federal Red Box, Current Production Gold Medal Match, Lake City M-852). but don't seem to like the heavier projectiles as much (Lake City M-118 173 grain). I hunt with both weapons and have had great luck with hand loads using 165 gr Ballistic Tips or 168 gr Berger VLD's loading them as close to M-852 spec as I can get, but would add that when I tried to go to 180 Gr Ballistic Tips that shot great in other weapons with 1-10 twists, the groups from both weapons looked like rat shit in a drawer!
Hope this helps
Regards
JHC