I have been looking at a  6.5 Grendel but I am not quite convinced that it is done the way I would do it. Seems to me that a 120 - 123 gr bullet is a bit to much weight and too long and that the case is a bit short.

Seems to me that a 6.5 bullet that was 85 gr or so would be pretty darn good and would allow you to grow the case. A larger case would give you more room for powder and that would push the bullet faster.

I looked at ways to do this and it looks like a 22-250 case would be great. Might need to leave it a bit short to keep the OAL to 2.26" so it would fit in an AR-15 receiver. The sticking point seemed to be the bolt face as a Grendel bolt would is too small.

Up come the 458 SOCOM and 450 Bushmaster bolts. They are cut to fit a .473 rim so it looks like they would both accommodate the 22-250 case.

So here are the questions:

Will both bolts fit a standard AR-15 upper receiver?

Would the ejection port need to be enlarged for a .473 case? Or just for the larger 450 and 458?

Is the ejection port cover longer than the cover for a standard AR-15 cover?

Would those bolts mate up to a standard AR-15 upper?

Is there anything else about the upper receiver that would need to be sized to fit the bolt and case? Not counting te mag and barrel of course.

Is there anything I am missing?

To eject 458/450/50beo brass the ports must be opened up.  I did not modify the ejection port on my 264lbc the Gredel's cousin.  The Dust cover works just fine if the port was done properly.  The cases are the same length as the 5.56 so port is same.  So long as you get the proper bolt it will lock up just fine on an ar15.  

Performance of the 6.5g is incredible.  It does not need to be fast.  123Amax is good past 600yds out of a 20" barrel.

If you use a standard .458S bolt with standard barrel extension then pressures cannot go higher than 35K psi.  The smaller head size of the 5.56 gives the same backthrust on the bolt lugs at 55K psi as does the larger head size of the .458 S does at 35K psi.  Head size, not bullet size is the limiting factor.
By using the .22-250 case head size you lose everything you think you are gaining by the 35K psi restraints.

You are better off sticking with the 6.5x6.8 or the 6mm x 6.8 or 6.5g, then you can run pressures up to 53-54K psi and get much better performance.

The only safe way to run a .473 case in the AR is with the Olympic special uppers, but that is a whole other discussion and proprietary platform.

Awww crap. LOL

Didn't look at that.

The 450 Bushmaster is only 40k. Crap

Looks like the only way to play bigger is AR-10.

You can also use a Young Manufacturing .473 bolt.   They are supposed to be rated for higher pressures than opened-up bolts.
Best,
JBR

I got a reply from YM. It looks at least possible.

Staff (Administrator) 4/28/2015 10:25:56 AM

Hi Steve,
We do not have a pressure rating on these bolts. What I can tell you is that we have a proprietary “Heavy Wall” design that adds .017” to the wall thickness between the bolt face diameter and the bottom of the lugs. The .458 uses a standard 5.56mm barrel extension and not a .308 extension.
Hope this helps!

I am thinking to have the bolt nitrocarburized as well.

Nice follow-up.  Thanks.
I am probably going to use the YM bolt for a Big Bore mule upper with a variety of barrels (.450, .458, .375, .338, etc).

Best,
JBR

Another update from Young:

Subject: 458 SOCOM bolt

The bolts are heat treated and hard chromed