Mauser J Bore

jlg15963 · April 26, 2005, 05:35 AM

I Have A Mauser Custom Sporter Made At The Oberndorf Factory In 1928. I Have Slugged The Barrel And Discovered That It Is .318 As Expected. Several Questions: Can I Use Standard 8x57 Brass To Reload? Do I Need A Custom Expander Ball On The Die? Where Can I Find Loading Data Or Can I Simply Use The Standard Data And Work Up Slowly. This Is A Fine Old Rifle With Heavily Engraved Reciever And Custom Carved Stock And I Would Like To Preserve And Shoot It Rather Than Rebarrel Or Rechamber. Thanks

Jlg15963

Ruger4570 · April 26, 2005, 07:25 AM

It appears you have a 8mm of the earlier type with a .318 bore and it was designated as a "J" type. The Germans later switches to the "S" bore that measured .323. The cases are the same other than the neck being changed to accomodate the newer bullet (.323). You can fire the older (J) ammo in the .323 rifle, with the resulting loss of accuracy but not the reverse. You should have no trouble using the current cases other than having to reduce/expand the neck and locating .318 bullets. There should be load info around on the net. I don't know the rifling twist but the older J bore shot a 226 gr. round nose and the newer S shot a 154 gr. bullet so there may be a difference in twist that might affect accuracy. You obviously have some homework if you want to shoot the gun, but it is a fine cartridge and right up there with the 30-06. Good Luck

jlg15963 · April 26, 2005, 09:27 AM

Thanks For The Info. I Have Already Located The Bullets At Buffalo Arms. I Think I'll Try The 150 Grain First And Work Up Slowly Using The Standard Data. I May Need A Lee Factory Crimp Die Or Perhaps I Can Just Remove The Expander Ball And Just Go Ahead And Seat The Bullets. I Haven't Tried Yet I Was Worried About The Brass.

Jim Watson · April 26, 2005, 12:21 PM

I expect standard 8x57 brass will do fine, IF your dies are right.
Size a case without expander ball and see if it will take a .318" bullet with normal bullet pull. If it does, great, you are lucky.
If it is loose, you need a real "J" sizing die, not a crimp die. You cannot crimp a loose bullet tight. Most reloading die makers are good about furnishing odd sizes like that at reasonable cost.
If it is too tight, you need a proper "J" expander ball something under .318" diameter. You can likely get one the right size from your die's maker or reduce the one you have.

US 8mm is loaded lightly, it is all descended from the 8mm Remington Special of the post WW I era, which had a bullet large enough for decent accuracy in a .323" but soft enough and lightly loaded enough to be safe in a .318" barrel. SAAMI load data is similar, with a maximum chamber pressure of 40,000 CUP. Due to the larger bore cross-sectional area you can still get velocity in the .300 Savage to .308 category, which ought to be fine for hunting.

Leftoverdj · April 26, 2005, 01:18 PM

Jlg, I have several hundred .318 bullets for sale. PM me for details.

April 26, 2005, 05:35 AM	#1
jlg15963 Junior Member Join Date: April 26, 2005 Posts: 2	Mauser J Bore I Have A Mauser Custom Sporter Made At The Oberndorf Factory In 1928. I Have Slugged The Barrel And Discovered That It Is .318 As Expected. Several Questions: Can I Use Standard 8x57 Brass To Reload? Do I Need A Custom Expander Ball On The Die? Where Can I Find Loading Data Or Can I Simply Use The Standard Data And Work Up Slowly. This Is A Fine Old Rifle With Heavily Engraved Reciever And Custom Carved Stock And I Would Like To Preserve And Shoot It Rather Than Rebarrel Or Rechamber. Thanks Jlg15963

April 26, 2005, 09:27 AM	#3
jlg15963 Junior Member Join Date: April 26, 2005 Posts: 2	mauser j bore Thanks For The Info. I Have Already Located The Bullets At Buffalo Arms. I Think I'll Try The 150 Grain First And Work Up Slowly Using The Standard Data. I May Need A Lee Factory Crimp Die Or Perhaps I Can Just Remove The Expander Ball And Just Go Ahead And Seat The Bullets. I Haven't Tried Yet I Was Worried About The Brass.

April 26, 2005, 07:25 AM	#2
Ruger4570 Senior Member Join Date: April 3, 2005 Location: Rochester, New York Posts: 2,136	It appears you have a 8mm of the earlier type with a .318 bore and it was designated as a "J" type. The Germans later switches to the "S" bore that measured .323. The cases are the same other than the neck being changed to accomodate the newer bullet (.323). You can fire the older (J) ammo in the .323 rifle, with the resulting loss of accuracy but not the reverse. You should have no trouble using the current cases other than having to reduce/expand the neck and locating .318 bullets. There should be load info around on the net. I don't know the rifling twist but the older J bore shot a 226 gr. round nose and the newer S shot a 154 gr. bullet so there may be a difference in twist that might affect accuracy. You obviously have some homework if you want to shoot the gun, but it is a fine cartridge and right up there with the 30-06. Good Luck

April 26, 2005, 12:21 PM	#4
Jim Watson Senior Member Join Date: October 25, 2001 Location: Alabama Posts: 18,535	I expect standard 8x57 brass will do fine, IF your dies are right. Size a case without expander ball and see if it will take a .318" bullet with normal bullet pull. If it does, great, you are lucky. If it is loose, you need a real "J" sizing die, not a crimp die. You cannot crimp a loose bullet tight. Most reloading die makers are good about furnishing odd sizes like that at reasonable cost. If it is too tight, you need a proper "J" expander ball something under .318" diameter. You can likely get one the right size from your die's maker or reduce the one you have. US 8mm is loaded lightly, it is all descended from the 8mm Remington Special of the post WW I era, which had a bullet large enough for decent accuracy in a .323" but soft enough and lightly loaded enough to be safe in a .318" barrel. SAAMI load data is similar, with a maximum chamber pressure of 40,000 CUP. Due to the larger bore cross-sectional area you can still get velocity in the .300 Savage to .308 category, which ought to be fine for hunting.

April 26, 2005, 01:18 PM	#5
Leftoverdj Senior Member Join Date: October 15, 2004 Posts: 934	Jlg, I have several hundred .318 bullets for sale. PM me for details.