Hello,
I figured since there are a few knowlegdable people on here I thought I'd ask here first. My brother inherited a mauser from his grandfather who brought it back after WWII. We couldn't find paperwork anywhere for it but have been told it is a Belgium Mauser. We can't find any marks to signify what caliber it is but we are guessing it's 7.65 Arg. We tried to chamber 8mm and it was too big and 7mm was too small. 30-06 would almost fit but still a no go. Is there anyway to tell what caliber it is chambered for? Maybe some markings I'm not familiar with? We have tried several times to find a gunsmith to gauge it but no one could tell us. He was just transfered to Fort Sill so he still has some looking to do around there but just wondering what info could be gleaned from here.  The rifle itself is in really nice shape and has this wicked bayonet with a nasty serrated edge on the top of it. He is supposed to be sending me some pics, I'll put up links when I get them. If nothing else it would be a nice display piece but we would both like to shoot it someday...

Any info would be greatly appreciated,
Thanks

Caliber likely will not be marked anywhere, although given what you said about trying different cartridges, 7.65 sounds like a likely suspect.  HOWEVER, given the number of Mausers that were converted to other calibers (either by militaries or private owners), you need to get a mold of the chamber so you can mic the chamber dimensions.  

As far as identifying the rifle itself, is there a crest on the front receiver band?  And what's stamped on the left-hand side receiver rail?  This will tell you where it was manufactured, at a minimum.

ETA:  You can take a chamber mold yourself.  I forget off the top of my head what the name of the material used is (I'm sure someone with a better memory will be along shortly), but I'm pretty sure Brownell's carries it.

pictures of the receiver, any stampings, and an overall picture of the entire rifle will help.

Cerrosafe

Brownells has it, melts at a low temp. Shrinks at first so it drops out, then expands back to size later.

Never used it, but have been meaning to pick some up.

fwiw, don't get too hung up on the "brought back from WWII" thing unless it's a standard k98, which would then be 7.92x57 or 8mm Mauser.  It's possible, of course, but unlikely.

Had a guy tell me last month that his grandfather brought back a rifle that he picked up off of a German sniper. It was a post-war Czech-made job, scrubbed crest and winter triggerguard and all, that he had just had shortened, drilled and tapped, and put in a synthetic stock.

Most of the "other caliber" military Mauser rifles came from South America in commercial imports in the 50s and later.

Post some pics for us, I'll bring my Mauser book home from school this week and try to cross reference for you.

Don

This.  I've got a couple Mauser books floating around here too, so I'm sure one of us can find it.