Big bore ARs

>16" was the base barrel length that SOCOM and Beowulf were designed around
Seems like these would be favored for a shorter bbl build. I'm left wondering how much velocity is lost for the .450BM from a 12" bbl or less?

>If so, .458 SOCOM is easily the winner, because there's much better selection of bullets/molds in .458 (rifle caliber);
This, 100%.

That said, keep in mind that if you want to build a big-bore AR you really ought to do it on a more durable platform than the standard AR-15; do it on something like the CMMG Anvil or the AR-10. The AR-15's bolt head must be machined out quite a bit to accomodate the larger rounds. That makes the bolt head weaker, so you have to keep pressures fairly low. What's the point of having a big bore AR if you are forced to cuck your loading? The AR-10's much larger bolt head makes it far stronger for big cartridges like this.

Pic related. CMMG Anvil bolt on the left (AR-10 style), normal AR-15 bolt machined out for .458 Socom on the right. Notice how thin the metal is on the right one, and how flimsy the extractor is, compared to the AR-10 style bolt head.

Attached: lar458_cmmgxbe_29.jpg (648x432, 30K)

>>.50 Beowulf for dick waving.
Yup, this would be great for the SCR lower build I'm thinking about. But I have to consider the practical side also...

I haven't seen any piston uppers.
But the only difference in uppers is an enlarged ejection port.
Bolt carrier is the same.
All 4 use a standard CAR buffer and spring.

I don't see any reason why you couldn't take an existing piston setup, open the ejection port with a dremel, replace the bolt, screw on a new barrel & handguard and be good to go.
The point of all of the thumpers was to use the existing platform with only minimal modifications.

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>What's the point of having a big bore AR if you are forced to cuck your loading
A great point, thx! This would increase the overall size and weight and the goal is still a pistol concept.

Yes. Idid find a custom built using an Adams Arms micro gas port with the same focus, but the concern was bbl profile and reaming the side walls of the gas block to fit. At that point I didn't understand why he wouldn't have made the bbl profile fit the gas block instead?

Thumper barrels are massive by nature.
I havent mic'd them out, but i would suspect a pencil Beowulf would still be thicker than a heavy 5.56.
Reaming the inside of a gas block is pretty straightforward. That's a quick 5 minute fix on a lathe. And since everything is based off of bore axis, everything would be perfectly aligned still.

It might be wise to keep the pressures low then. The recoil firing full-power rounds like these from a pistol would be insane.

The CMMG anvil is probably the optimum choice if you wanted to go full power. It's a hybrid design that has the same length as an AR-15 and takes AR-15 mags, but it has the larger AR-10 bolt. It's a little bigger than an AR-15 receiver because it's thicker/stronger, but it's not as big as a full-on AR-10. And, IIRC, it is available in a pistol config.

Here's a recent article OP found on a 7"bbl .450BM Windham Weaponry saying 21% velocity drop from published MFG data (9"w/brake, it goes back a forth).

americanrifleman.org/articles/2018/11/30/tested-windham-weaponry-450-thumper-ar-15-pistol/

Interesting, I'll look into that. I need CCMG for a PS90 sbr project anyway. I note the .50 Beo uses the 7.62x39 AR bolt and wonder if pressures are really an issue for that cart/bolt combo?

*artical notes the drop puts the .450BM into .454Casul territory

Don't want to scare you, but....
Pic related.

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I'm not sure what you are trying to imply, user.
I'm talking about the length of the CMMG Anvil *receiver*, not the length of the loaded cartridges.

No fear here, if by that you mean recoil? NP I enjoy bb handguns since '95 and have several.!

OP also found this for .450BM 10.5" upper for under $200: deltateamtactical.com/450-Bushmaster-Barreled-Upper-Receivers-Ar-15_c_494.html

But I'm not familiar with this company's rep?

Round is seated in the chamber. Once the bolt lugs are locked in, there's no difference between the pressure capability of a Beowulf or a 7.62x39.

As I might expect as it (.50beo) was designed to use that bolt. So the stouter Anvil bolt for the .450BM does make sense, but for the shorter pistol length bbl higher power/pressure ammo wouldn't be applied. This platform will be spec'd around factory pressures ammo, so...

That company also does business as Davidson defense and yet another company.
They buy bulk runs, put together a kit, sell them until they're gone then buy whatever else they can get.

I have no doubt that it will function.

First 3 on your link look like the type that the handguard glue onto the barrel nut then clamp down. I'm not sure how the 4th attaches.

I've seen people who have done the glue on and don't have failures, but they're a nightmare to get off for mods or repairs.

4th looks like handguard plate/nut is indexed then handguard is screwed on from the receiver side.
Probably the safest bet between the 4.

Incorrect.
Some of the pressure acts on the chamber, but some also acts against the bolt. The RIM diameter of the 7.62 x 39 and the .50 Beowulf are the same, but the CASE diameter (where the pressure from the powder is pushing against) is not the same.
7.62 = .447 inch base dia. = .157 sq. in.area
500 Beo = .535" dia = .225 sq. in.
That is a 43% increase in area, which corresponds to a 43% increase in the force that the bolt must withstand during firing, assuming the same pressure in both cartridges. You would have to down-load the pressure in the Beowulf by that same amount (43%) in order to have the same bolt thrust as a 7.62x39.

Because of this, rounds like the .500 Beowulf are downloaded in pressure to keep them safe. .556 and 762x39 are 50,000 psi plus cartridges. .50 Beowulf is 33,000 psi:
hendonpub.com/resources/article_archive/results/details?id=3631

This is what user was referring to in If you use the stronger platform with the bigger bolt head then you can load to higher pressures than you can building on an AR-15.

>This platform will be spec'd around factory pressures ammo, so...

I was the guy who was recommending the Anvil earlier. If you're only going to use factory pressure spec ammo then there's zero reason to use the Anvil or AR-10 frame; use AR-15 and it will be cheaper, lighter, and more options for you to pick from.

Just know that by limiting yourself to the factory pressure specs you're also missing out on a lot of potential performance out of the cartridge.

There are tabs on the handguard to "stabilize/align" on the upper for the first 3.
If the barrel nut has grooves for those 2 screws on the bottom to slide through, it would be a stable design.
But unfortunately I've seen all the different ways they attach and can't tell from the pics.
I haven't seen the glue ons for a couple years though so it might be worth a gamble.
Or call them and (maybe) someone can clarify.

Its more complicated than that.
7.62 has a shorter case (x39), which means more pressure is exerted on the base than a cartridge that had the same diameter but the length of a Beowulf (12.7x42).

My state only allows straight wall cartridges for deer hunting. This is my second year deer hunting and I was thinking I'd get a 450 Bushy upper for it. 450 over Beowulf right?

That's nonsense.
Pressure acts on all surfaces of the "container" equally. That's one of the most fundamental concepts of physics. Pascal's law. The pressure on the base of the cartridge, on the walls of the chamber, and on the base of the bullet are identical.

Oooo
Let's do bottleneck vs straightwall next.

Thx, glued hand guards don't sound too appealing. But for the cost, that is...

Gotcha and I have no doubt about that! But hotter loads in my prospective pistol, esp. with that grip, aren't expected or necessarily desired! In a carbine or full length rifle, for a custome build, I wouldn't have it any other way!

OP here, this is where my recent research is leaning. But balistically they are all so very close and you could do just as well or better with a .45-70 Marlin M1895. But I've got one of those and it's not a semiautomatic Howdah pistol!

OP agrees with this as a true statement. OP hopes not!! ;)

Keep thinking Howdah. The desired goal of this big bore AR pistol is range toy, HD and as originally developed and used, PDW for tigers jumping into my safari basket on top of an elephant! Most likely in that order...

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I could just puss out and get the 20ga Pedersolli and use 20ga slugs: cabelas.com/product/Pedersoli-Howdah-Hunter-Ga-Pistol/740261.uts

Nah...

458 socom and the beowolf have autistic case designs. the beowolf has extremely limited bullet selection and they cost more. 458 socom is named "socom"...literally poser faggotry.

450 bm is the way to go

>beowolf has extremely limited bullet selection and they cost more
I'm seeing $1.10-2.50/rnd factory and components available from Graf and Sons and Midway, didn't look too hard really.

But one of your concerns is the case shape is "autistic"?

yes. autistic, both of them.

Ok, thx. But can you say why or define the context as it applies to metallic cartridges, please?

the retarded shoulder on the socom
undersized casehead on the beowolf

By "undersize", do you mean like, "hip to waist ratio", as in on a woman? As in it's not what you like to see?

Do you know the etymology of the term "funny car"? Yet, are they fast?

its self explanatory. if you didnt get it you're a moron.