I have an opportunity to purchase a pre-war Heym combo gun with 16ga over 7.8x57 (stamped on the barrel). It has what appears to be Deluxe grade engraving, good wood - has not been a safe queen and has some handling/use marks. He's asking $1500.00 USD

Questions:
1. I have looked through my reloading books and have done an Internet search to try to find out if 7.8x57 is actually the same as "standard" 8x57 Mauser without much in the way of 100% conclusive answers. I don�t want a �show gun� I want �a shooter� and want to be able to find reloading components without having to purchase custom dies and brass.

2. I know the Heym name is excellent and is his price "reasonable"? (if I can find reloading supplies).

I have read and seen the "standard" 8mm listed as a 7.9x57. Possibly the 7.8 is the .318 bore version? Try posting in the Europe forum, may obtain some help there.

I expect you will have to slug the bore to find out if the rifle is a .318" or a .323" unless there are other proof marks (usually on the underside or below the wood line). Otherwise it is definite maybe.

jim

Yep, the "standard" 8mm Mauser is a .323 and is known as the 7.92 x 57, and is so marked on the barrel at the ring of some of the Mausers. The 7.8 is the older "1888 Commission rifle" chambering, and takes a .318 diameter bullet. Whatever you decide, DO NOT shoot regular 8mm Mauser stuff in that gun.

Wayne

Actually, and you need to check it for yourself before taking my word for it, American factory loaded 8x57 ammo is loaded with a compromise bullet that'll work in either the J (.318) or S (.323) bores. It's also loaded to pretty anemic performance levels out of deference to weaker non-M98 actions.

I know it was done "back in the day", I don't know for a fact that it is still the case, or if it was done by all manufacturers.

Yep; Per Macks "Cartridge Case Measurements" the 7.8x57 is for the 1888 Mauser.
Now maybe someone could clear up the history of the groove dimensions. I have read that the 88's used an oversized bullet
that wouls swage down. To aid this the forcing cones were tapered. I have seen 1888 Mausers with this. Later they increased the groove depth keeping the same bore size.
At this piont the designated the differences as S & J sizes.
I have also read that the Military used the same bullet with
both groove depths.
Any Mauser historians out there?.
Thanks!