My 16x16x7.8 drilling has me baffled as to the actual caliber. Somewhere between .311 and .318?
Anyone able to tell me what 7.8 relates to?
Thanks
Frank

Possibly 8x57JR....which is .318 bore.

Frank - can you determine the case length , and type - like , is it a bottlenecked case?

Brad Dixon lists several 7.8 calibre rimmed case-types in his book "European Sporting Cartridges" , and a bit more information might narrow it down a little.

Thanks for that lead. I will need to do a chamber cast to be sure.
Frank

I take it the 7.8 is mm's? If so, 7.8mm = .30708".

Thanks Craigster. I had to check since I got confused after reading this.
http://forums.gunbroker.com/topic.asp?TOPIC_ID=117178

German proofs of the period called for marking the _bore_ diameter, not the _groove_ diameter of the barrel to the nearest tenth of a mm. A rifle barrel marked 7,8mm will typically be a "J" bore (.318" diameter) 8mm of some sort, but the actual cartridge identification will require a chamber cast and the groove diameter is most likely to be close to .320" in my experience.