I have a friend who wants start loading for his brothers 8mm due to the high cost of good factory ammo. i know there are different bore diameters and my question how do you tell which is which?

What 8mm rifle does he have, what is the condition and has it been checked by a competent gunsmith? The earlier 8mm rifles had .318" bore diameters and the later ones (after about 1905) had .323" bores. Not all German military rifles were converted and some sporting rifles retained the smaller bores.

If your friend's rifle is from WWI or WWII it should be ok if it is in good condition and has been verified by a competent gunsmith. Hope this helps. All the best...
Gil

IF it's a militray gun, then it's pobably the larger sized bore...they offically switched over a LONG time ago (somehwere before WWI, but some of the old small bored rifles did get used in WWI). For whatever reasons (and there were some issues dealing with the treaty of Versailles), commerical.custom made European rifles often used the smaller bore (.318" vs, the modern ..323")..and sometimes neglect to mark the barrel as a "S" (small bore...the larger bore is a "JS").


IF in doubt, slug the bore...in fact, slug it even if you THINK you are sure..this site has some good slugging instructions in the Tech. Notes.

I haven't seen the rifle yet, but he described it as a military rifle that shoots pretty good with factory ammo. I will do some further investigation into the matter

Slug it. Peace of mind.... you never know. Old guns get modified, rebarreled, who knows what. It's the first thing that I did with my turk.... was glad to see that it had a .323" bore.

Anyway, there is plenty of 8mm data, just read the fine print to see how hot it's loaded. I know the Nosler manual is full-tilt with their loads....

IIRC the 8x57j is the small size, the 8x57js is the larger bullet. The j takes the place of i in the Deutsche alphabet, and stands for infantry. Possibly the biggest potential problem is the 1888 Commission Rifle, far as i know they all had the .318 bore, and were pretty much identified by the sheet metal shroud around the barrel. At one time they were available in stores like K-Mart (in Austin TX, anyway) for $69.95 or so. Slugging the barrel is always good advice, tho, and the best way to make sure.

The original 8mm (0.318) Mauser dates from 1888, the "modern" 8mm (0.323) Mauser dates from 1905. Most of the hate and discontent over the two bore diameters stems from the 1888 Mausers and from European commercial sporting rifles which continued with the 0.318 bore right through the 1920s and 30s. If your rifle is of German, Austrian, or Turkish descent, i.e., not a Kar98k. itwill be best to slug the bore for safety. Of course, those small bore Mausers are the reason for the underloaded US factory ammo. You can trust a Post-World War II M98, or for that matter a VZ-24, FN 1930, or FN-1948 as well to be 0.323 bore.


Also, look out for 8x60mm caliber Mausers, rimmed and rimless. They were made as commercial sporters between WWI and WWI and they definitely exist in both bore diameters. A nice cartridge, but another case for "slug the bore first!" Norma made 0.318 ammo for this chambering into the 1960s.