308 Norma Magnum to 300 Winchester Magnum

M

mapsjanhere

New member
A friend of mine has a very nice FN Mauser in 308 Norma Magnum. With the limited availability of the 308 NM it would be nice to rechamber into 300 WM. From my research both cartridges have identical dimensions but for the NM shoulder being 0.11" shorter. What is basically a short chambered 300 WM. Can anybody see a problem in that conversion?
 
It was my rifle, I'd just buy .300 Win. Mag. cases, full length size them in a .308 Norma Mag die, trim them to length then load them with data for either the .30-.338 Win. Mag or .308 Norma Mag and shoot them. The Norma case was favored for long range matches of the Win. Mag anyway; better accuracy with new cases and the barrel lasted a bit longer. It was one of the favorites in long range benchrest when that discipline started.

Otherwise, the Norma chamber may not completely clean up with a .300 Win Mag reamer at the Norma shoulder point as well as the throat.
 
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It was my rifle, I'd just buy .300 Win. Mag. cases, full length size them in a .308 Norma Mag die, trim them to length then load them with data for either the .30-.338 Win. Mag or .308 Norma Mag and shoot them. The Norma case was favored for long range matches of the Win. Mag anyway; better accuracy with new cases and the barrel lasted a bit longer. It was one of the favorites in long range benchrest when that discipline started.
Click to expand...

I really like that plan!
 
I have to agree with SCORCH, if there is a problem with the 300WM reamer cleaning up the 308 Norma chamber is would be caused by two different neck diameters. 7mm57 Mauser chambers have been up graded to 280 Remington, it is not often the reamer of the 280 Remington will clean up the ‘generious’ neck in the Mauser chamber. Then we go back to the 308 Winchester, some believe the 308 Winchester is a short 30/06, that is until they upgrade the 308W chamber to 30/06, upgrading the chamber is when they discover the difference, the case body of the 308W has less taper than the case body of the 30/06, meaning the 30/06 reamer will not clean up the 308 W chamber. The part that does not get cleaned up in the 308 W chamber is the shoulder/case body juncture. Fired cases will have a ring around the case that is about .011” high.

F. Guffey
 
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