late 2011 after hunting season I had gathered enough parts for a build I wanted to try out. An AR15 in 357Max only without the rim. I had a cheap $30 357/38 barrel blank, barrel extension, spare upper, BCG and enough extra parts to finish up an upper. Didn't want to pay for a custom reamer to test it out in case it didn't work out. A standard 357Max reamer cuts a leade starting at the case mouth so you can also shoot shorter 38 and 357 ammo. Since this would be headspacing off of the case mouth I needed a reamer that would cut a case mouth step. After making a few dummy rounds a reamer print was made and from the reamer print I machined a reamer on my lathe and mill. Standard 357Max head space gauges will not work. Being a straight walled case the headspace gauges are easy to make as they can be as simple as a cylinder of a certain length, but an extractor groove makes them more usable. Cut the chamber and installed the barrel extension verifying headspace. The feed ramps were opened up with a 3/8" carbide ball end mill, but I've since gone to a modified center feed type. The magazines need the bullet guides removed from the front of the mag so the cases can double stack which is easy to do on Pmags using a dremel and a sanding drum. The test barrel went well and cycled several different bullet types so the test barrel was sectioned and a new GMB .358" 1:14" blank was purchased for a better build.

that's pretty cool .. what are you getting out of 158gr hjp?

Made a pistol and hunted with it in 2013, and when the DNR changed the regs and allowed straight walled cartridges in 2014 I took the 357AR out. After that We made one for my son who has used it the past 3 seasons. Last is a pic of his first deer with it, a doe at 142yds. Slight angling broadside shot that broke the opposite shoulder on the way out. His hunting load is a 180gr Hornady SSP at 2140fps out of his 16" barrel.

jeffeosso, 158gr XTP's can be run up to 2400fps in a 16" barrel. We shoot alot of them as plinking rounds at around 2290 fps.

thanks! - This is a really nifty concept -- i love 35s, i like ARs, and adore wildcats

It's been a fun little round with the only PITA being making the brass from 223/5.56 cases. Recently Starline came out with some 223 basic brass that only needs trimmed for length and reamed with a .355" reamer. I set my Forster trimmer up with a reamer pilot and a drill adapter. It only takes a few seconds per case using the starline cases. https://www.starlinebrass.com/...Caliber-Designation/

Here's the print for the reamer I've been using the past 4-5 years.



Originally I had a longer freebore on my test barrel which I knew was too long so it was shortened to .075" freebore. As soon as I started using different bullets I discovered that the .075" freebore was too so so it was changed to .150". If you're having a reamer made, Manson reamers has both the 357AR (.075" freebore) and the 357AR-2 (.150" freebore) reamer prints on file and makes excellent reamers. The longer freebore lets you set 180gr XTP bullets behind the rear crimp groove for more useable case capacity as well as seat heavy and cast bullets out a little further so they don't take up as much case capacity which is more noticeable in a small straight walled case than in a bottleneck case. Make up dummy rounds for whatever you know you're going to shoot or may want to shoot and modify your freebore length accordingly.