Originally Posted by Vikingdad
My buddy has a 7.62x54r upper for his AR (not exactly sure why he went this way but nevertheless...) and I was talking to him about reloading for it. Should we slug the barrel to size it or what?
Just call the mfg. of the upper they can tell you the groove dia. which could be anything from .308 to .311,it just depends on what they based there specifications on when they designed the upper.
Mosin rifle groove to groove dia. varies widely even in rifles made in the same country especially during wartime conditions when mass producing rifles was more important than sticking close to the original design and tolerances.
The Finnish Mosin's we designed from the ground up more refined and to be more accurate,your typical Finn Mosin will have a groove dia. of .309.5" .308 dia. bullets work well in these rifles. Your typical Russian Mosin bore can run anywhere for .310 to .316 those two numbers are in the extremes,most generally slug out at .311 to .312 my M44 is .312 as well as both my brothers two 91/30's. The only sure way to know and being able to pick the best dia. bullet which does affect accuracy,velocity and pressure is to slug the bore yourself http://7.62x54r.net/MosinID/MosinSlug.htm
Reloading manuals vary widely aside from powder and primers used,bullet dia. varies as well from one manual to the next. Reloading manuals base there data on different criteria some use the actual rifle,some use a universal receiver which basically uses a chamber insert for a specific cartridge. A .308 dia. bullet is a safe choice in any Mosin,no problems with chambering or pressure issues. If you load an oversizes bullet say a .312" in a 309" dia.. Finn rifle chambering the rd. might not be a problem but you will have pressure issue loading that larger dia. bullet at near or Max. load density. I suspect thats why so many manuals list the .308 dia. bullet it take away much of the liability of the company from individuals that either don't know or care to research there particular rifles specifications.
On a side note my Lyman #48 & #49 manuals list the groove dia. as .313" using the Finn SAKO rifle,while my old Lyman #45 manual list the groove dia. as .310 using the US MADE Westinghouse Mosin. My M44 Russian which slugged out at .312" groove to groove as well as my brothers two 91/30's shoots the .311" dia. bullet in the 150 gr. range best .308" don't shoot well at all. With cast,bullets sized to .314" have provided the best accuracy.