.357 ar?

[DaveyMG]

So a guy on another forum got me to thinking about this hairbrained, wildcat idea... He actually built it, and has a functioning version of the idea, which I would like to replicate. For the ammo, he used once fired .223 brass, cut to the shoulder, and 9mm (.355) flat nose projectiles. The bullets can be used in standard polymer mags, and he claims feed very reliably. My thought at the moment is on the chamber reaming. I know an 8mm taper pin reamer produces the identical taper and diameter (if you stop cutting at the right depth) as a 9mm round, a .223 case has approximately .020" of taper, if cutting off the neck, and basically creating a 9mm magnum round (or call it .357 AR max, or .355 magnum or whatever you decide to call it) is there any reamer that will match this taper? Say, if a guy wanted to build 3 or 4... I know I could make a D reamer, but was hoping to find a more suitable (repeatable) tool. Thanks for any input or suggestions!

 

[DaveyMG]

Well it looks like the #7 taper pin reamer might just do the trick... It has .020" of taper PER inch, and the .223 case normally has .022" taper over 1.438" length... But I know a local tool grinding and regrinding company that could probably resharpen it with the proper taper and even give me a nice pilot to the end... And it'd probably be 1/4 the cost of a full on custom reamer...

 

[rcmodel]

Taper pin reamer will not work.

You need a proper chambering reamer to cut the headspace shoulder in the end of the chamber.

Otherwise, there is nothing to stop the round from seating too deep, and either not firing at all, or blowing the case head off if it does fire.

rc

 

[DaveyMG]

Ok, so after reading a bit more on it, the case is actually formed into a straight wall, .377 the entire length. And the reamer he used just has a 45 degree lead angle that the case mouth rests against, so looks like maybe modifying (regrinding for a pilot) on a V letter size reamer might work... Thoughts?

 

[OARNGESI]

Would this be better than a 9mm ar?

 

[DaveyMG]

Oh yeah. The one I am contemplating is more easily defined as a .357 Maximum rimless. (Think 9mm, but with a 1.75" long case, and approximately 180gr bullet) it makes the 9mm cartridge look like a .22, next to a .44 magnum. I'd share a pic of the cartridge, but for some reason my photobucket isn't working today. The cartridge is the same overall length as a .223 round. Just with a straight walled case, and a 180gr soft point, boat tail, .358" projectile.

 

[BBBBill]

If you want to do it, the do it the right way. Get a proper reamer ground to the correct specs for that wildcat. Trying to cheap out by modifying some other kind of reamer is going to be an expensive exercise in futility and wasted money. You will have other issues to work through as with any new venture in gunwork. No need to unnecessarily cripple yourself right up front.

 

[dsink]

Kind of sounds like the old 351SL round. You might want to take a look at it.

 

[hentown]

Sounds like I really prefer my .300 Blackout.