450Bushmaster.net

Long time 357MAX user here. (Bought my first one early 1980's right after it was "invented"..

Friend on another Board has been working on a 357 AR for couple years.

VERY happy to see Winchester pick this one up. it should duplicate the Max ballistics maybe plus a lil!

Anxiously watching this one!

CW

To parrot what was said in the other thread, the rebated rim is a "deal breaker for me"
Winchester makes sure you can't use Starline 223 Basic brass or any .223 brass for that matter, without running each one through a lathe or neck turner to reduce the rim diameter. Don't even try to explain that move as an attempt to reduce bolt thrust. IMO, greed plain and simple. That's assuming the rifles uses a special bolt and extractor. If they squeek by with the more generous .358 bolt and extractor, then they're back in my good graces as that would negate the rebated rim. Not unlike the 450b working with a .473 bolt and extractor. Remember Hornady / Bushmaster's sneaky trick?

Hoot

Hoot wrote:To parrot what was said in the other thread, the rebated rim is a "deal breaker for me"
Winchester makes sure you can't use Starline 223 Basic brass or any .223 brass for that matter, without running each one through a lathe or neck turner to reduce the rim diameter. Don't even try to explain that move as an attempt to reduce bolt thrust. IMO, greed plain and simple. That's assuming the rifles uses a special bolt and extractor. If they squeek by with the more generous .358 bolt and extractor, then they're back in my good graces as that would negate the rebated rim. Not unlike the 450b working with a .473 bolt and extractor. Remember Hornady / Bushmaster's sneaky trick?

Hoot

if that chamber spec is right with a .392 base, the rim could still be 223 size (.378), hence rebated, just not a lot.

would love to have a round I could pull down and measure up so we all can sleep at night!!!

Right, it would not be smart to make a new bolt for this thing. So I assume it's going to be a .223/5.56 bolt. At that point, you probably still couldn't use .223/5.56 brass because case head growth/failure could be an issue.

Edit - Just watched a video on youtube where CMMG says it will use a standard .223/5.56 bolt. https://youtu.be/Q5VMr3Yh8hk

Also watched another one where the rep states .357 bullets. https://youtu.be/s5XfTT1_VzI

Using QuickLoad, I modeled a 1.71" case with an estimated fired case capacity of 35gr H2O. Pushing a 140gr Barnes XPB ahead of 26gr H110 at 2.20 COL, it yielded a predicted MV of 2377fps from a 20" barrel. All my AR's have a minimum barrel length of 20", so I used that. Obviously, shorter barrels = lower speeds. This caliber model has not been justified against actual field results. In practice (see sig), it could prefer a different powder and/or produce different speeds. I used a max chamber pressure of 44962 psi, per the CIP spec for a 357 Maximum. In this model, the 26gr H110 represents a charge of 95% capacity and burns at 97.8% by the time the bullet exits a 20" barrel. That burn rate is in the vicinity if ideal for a straight wall case from my experience. All else being equal, the same charge of Lil Gun burns all the powder in a 16" barrel for the same resultant velocity but at a chamber pressure that's slightly higher than the H110.

All these variables serve to demonstrate that we just don't know until some field reports start coming in.

Hoot

Yeah, we need more info. I’m thinking they’re going to push 50-55K PSI

Bmt85 wrote:Yeah, we need more info. I’m thinking they’re going to push 50-55K PSI

I don't know if their lawyers are as skittish as Hornady / Bushmaster WRT max chamber pressure in an AR 15 platform. If it was a bottleneck, maybe they'd go that high but this is all wait and see territory.

Hoot

Well, IIRC, bolt thrust is looking at the peak pressure in relation to the internal area of the case head. So if the case head is about the same size as .223/5.56, I would think they can similar pressures. They may drop it a little, because of the lawyers, but they should be able to keep it higher than standard 450B. My thoughts anyways.

More info

SAMMI has approved the cartridge!

https://thereloadersnetwork.com/2019/01 ... shot-show/

Hoot wrote:

Bmt85 wrote:Yeah, we need more info. I’m thinking they’re going to push 50-55K PSI

I don't know if their lawyers are as skittish as Hornady / Bushmaster WRT max chamber pressure in an AR 15 platform. If it was a bottleneck, maybe they'd go that high but this is all wait and see territory.

Hoot

the brass and bolt for a 223/556 is designed for what 60k PSI?



would tend to make one believe that 50-55k psi should be well within the wheel house of the new cartridge then. with wiggle room on the top.