BigBlue 94
Member
Im in the thinking process of a ludicrous idea. I want to build a light weight bolt action upper that will fit on any standard AR-15 lower. The bolt design lends itself well to a straight pull bolt action design, imo. No reason for making it other than for fun.
I want to chamber it (here is the ludicrous part) in 256 Winchester Magnum. The 256 WM, for those unfamiliar, is a 357 magnum case necked down to .257" and plugged with a 60 grain bullet. Slings it down range at about 2500 fps out of a 16" barrel.
This leads to my title question. The 7.62x39 and Grendel bolts have the correct .44x" rim diameter but the face is anywhere from .125" to .136" and the 256 WM has a rim thickness of .060".
My initial thought was to weld the face up a bit then cut the bore back to .060" on my lathe. But that will destroy the heat treatment on it and i have no means to restore that hardness. And i would need a .060" longer firing pin and ejector.
My second thought was to make up the .065" difference on the face of the breech. Essentially facing .065" off all but a small ring around the chamber that would fit into the bolt face with the cartridge rim. But that leaves me with a small ring only .032" thick around the base of the case. This sounds much easier than the first method.
I thought about taking .060" off the front of the bolt, lugs included, and spinning the barrel in another .060". But with a 50k psi cartridge rating, im not so sure thats wise. This seems like the easiest route
Thoughts? Criticisms? Am i fool and should i just build one in a standard caliber?
I want to chamber it (here is the ludicrous part) in 256 Winchester Magnum. The 256 WM, for those unfamiliar, is a 357 magnum case necked down to .257" and plugged with a 60 grain bullet. Slings it down range at about 2500 fps out of a 16" barrel.
This leads to my title question. The 7.62x39 and Grendel bolts have the correct .44x" rim diameter but the face is anywhere from .125" to .136" and the 256 WM has a rim thickness of .060".
My initial thought was to weld the face up a bit then cut the bore back to .060" on my lathe. But that will destroy the heat treatment on it and i have no means to restore that hardness. And i would need a .060" longer firing pin and ejector.
My second thought was to make up the .065" difference on the face of the breech. Essentially facing .065" off all but a small ring around the chamber that would fit into the bolt face with the cartridge rim. But that leaves me with a small ring only .032" thick around the base of the case. This sounds much easier than the first method.
I thought about taking .060" off the front of the bolt, lugs included, and spinning the barrel in another .060". But with a 50k psi cartridge rating, im not so sure thats wise. This seems like the easiest route
Thoughts? Criticisms? Am i fool and should i just build one in a standard caliber?