450Bushmaster.net

wildcatter wrote:

Texas Sheepdawg wrote:I was contemplating a 284 case cut down like the 450B
but instead of a .452, I wondered what if I could create
a shouldered case with the same COL as the 5.56mm
So it would feed through a standard AR 15... But
Necked to a 41 caliber or 10mm 150-185 grain.
Just a fantasy cartridge.... I haven't had this in my head
long enough to actually put it on my mechanical drawing
Table yet.

Your fantasy is going to come true, in both 41 &40 and way more calibers, try everything from 475 to 17 cal. Those 90gr .224 Sierra MatchKings ought to be interesting, but then again, I've got some other cartridges, not based on the 284 that will knock your socks off, wait until you see "My" version of the 50cal (remember after the socom/beowulf folks interviewed me, they decided to try and one-up me, however, their mere low pressure pistol case, with no-usable parent case, extreme high cost, and terrible availability, falls far short) and, .."Coming to a Godzilla near you", try a .530 bullet, at our speeds..t

That's awesome!

I've thought about a .284 case necked to 6.5 in an effort to get a little more velocity than the Grendel. I would love to duplicate the 6.5 x 55 velocities with 140 grainers out of an AR-15 upper. My concern is that the introduction of the shoulder will increase bolt thrust, intuitively I'd think more shoulder = more bolt thrust, so the question becomes would the larger case capacity lower pressure enough to offset the increased bolt thrust enough to get more velocity, or is the smaller shouldered Grendel a better balance without going to the RAR bolt and upper. Also, if you pay another pound of weight, you can chamber the .260 or the Creedmore in an AR-10 platform with no worries.
BD

My understanding is bolt thrust is a function more of the inside diameter of the base. Acts just like a piston. There are aftermarket bolts out there now that function with a .473 diameter case head (ala 284, ect) in a AR15 bolt carrier. They are not just an 5.56 bolt opened up. But it is a custom build and development wise we are pretty much on our own. I really, really want to neck the 450B down to a 35 caliber.

Siringo wrote:My understanding is bolt thrust is a function more of the inside diameter of the base. Acts just like a piston. There are aftermarket bolts out there now that function with a .473 diameter case head (ala 284, ect) in a AR15 bolt carrier. They are not just an 5.56 bolt opened up. But it is a custom build and development wise we are pretty much on our own. I really, really want to neck the 450B down to a 35 caliber.

Ooh Ooh! 35 WSSM equivalent. Now we're talking!

Hoot

I have been looking at the WSSM's, but a 450B to a 35 caliber would be between a 35 Remington and 358 Winchester. There are so many possibilities with the 450 case, but the problem is the bolt.

Siringo wrote:My understanding is bolt thrust is a function more of the inside diameter of the base. Acts just like a piston.

That is the basis of one widely used theory. However, if it were truly that simple, big bore revolvers like the .454, .460 and .500 would lock up after every shot, and .22 hornet revolvers would not. Since the opposite is true in practice, I'm thinking that case taper and shoulder have a lot of influence on bolt thrust.

BD

the last time i took the .450B out i shot about 80 rounds through it one afternoon and let a couple of other people put smiles on their face including my permanent grin, it is top dog as far as im concerned for accuarcy of the big bores....
but my personal needs go beyond that... i think the trend for short action cartridges other than the .223 is going towards a more viable hunting/sporting ar, meaning the widely used .308 in the ar-15 format... the .308 parent cartridge makes the .243 win, .260 rem, 7mm-08, .308 win, .338 federal(nice), .358 win, and my version of the .40 carbine which uses the 6mm rem parent chamber fits perfectly in all mags and 1 50 round drum i tested , also tested the 6mm rem of course and the .220 swift in the straight mags...

get yourself a .308 based ar-15 and you can build a rifle firing any of the fine cartridges listed above just by changing the barrel... you might have to tweak the buffer and spring specs... heck if i can make ar operate without any gas tube i think most of you could figure it out... give er

just a thought

happy holidays

cheers

Like a 30 Remington AR necked up or down.

Hoot wrote:Personally, I'd like to see a .44 caliber thumpette based upon a .308 case cut off at the shoulder. Brass would be abundant and would not cost $1.00 each, which pretty much guarantees no manufacturer would consider it. On second thought, they could modify the .308 case such that if you wanted to make your own from surplus .308 cases you'd have to buy reamers and perform tedious touch labor to recreate it.

EDIT: The .308 case diameter where the shoulder starts is the same as the .444 marlin (.453) so seating a .44 caliber (.429) bullet has already been demonstrated. It wouldn't hold as much powder as the .444 Marlin since the case would only be 1.56" long as opposed to 2.25, but still a lot more than the .44 Magnum at 1.28".

Hoot

Check out the 44 AutoMag, that is exactly what you described.

lucasphi20 wrote:Check out the 44 AutoMag, that is exactly what you described.

Yes and No. The approach to making it would be along the same lines, but the Automag case is the same length as the .44 Magnum (rimmed). I was thinking a longer case for more capacity and velocity. Also, in cutting down the .308 case for the Automag specification (1.29") the case wall starts getting pretty thick down there and would require reaming. By cutting the .308 case at the shoulder around 1.56", the case wall is not as thick (.426").

This puts it more in perspective:


Hoot