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Posted: 6/28/2026 1:21:21 AM EDT
| I know that this will cause a few eye rolls and "he should know better" responses, but here goes. I've compared the bottom end of the .450 BM and .45 ACP. They look to be the same width. Since my experiment with the 45 ACP projectiles in reloaded .450 BM worked out, I got to wondering if it is possible to fire the pistol round from the rifle with a chamber adapter and of course a grease gun magazine adapter in the mag well. |
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I don't think anything exists. Greasegun magazine magwells are wider than a standard AR-15 magwell. There have been several low production runs of Greasegun magwell AR lowers. Uzi magwells using ProMags will fit a standard AR-15 magwell, as will Macon Armory's proprietary mags and magwell adapter - @Mad-Machinist @MadMachinist @Mad_Machinist |
I use an old MGI lower with the GG magwell as pictured below: They are available today from https://hydraweaponry.com/product/hydra-h3-grease-gun-modular-magazine-well/ |
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Originally Posted By jreinke: Not to mention the fact that a 45 APC bullet wouldn't even be engraved by the rifling: .451 < .458. 450 Bushmaster uses a .452 bore, identical to the 45 ACP. It does not use the .458 bore used by heavy rifle calibers, and by 458 SOCOM. |
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It was not taught by the State.
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| My first reloads for 450 Bushmaster used 45 ACP Hornady XTPs. I think that I should add that I am asking about an adapter that allows me to fire 45 ACP from a 450 Bushmaster barrel. Due to the shorter cartridge casing projectile OAL there would be some free bore jump from the chamber to rifling. |
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Interesting idea. Years ago, I shot some 9x19 in a Destroyer carbine. These are generally chambered in 9x23. Cut a piece of 9x18 steel case and pressed it in the chamber. It would fire 9x19 without issue. You may be able to do this with a piece of .450 BM brass? I load .450BM subsonic for a bolt action. It would be cool to shoot 45 acp through it. |
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Originally Posted By Hilljack: Interesting idea. Years ago, I shot some 9x19 in a Destroyer carbine. These are generally chambered in 9x23. Cut a piece of 9x18 steel case and pressed it in the chamber. It would fire 9x19 without issue. You may be able to do this with a piece of .450 BM brass? I load .450BM subsonic for a bolt action. It would be cool to shoot 45 acp through it. That is kind of how I see that happening with the 450 to 45 conversion. I don't need for the gas tube to work as 45 is blowback anyway. I am thinking on the idea you used in the Destroyer Cabine. That would definitely allow the .45 acp cartridge to head space correctly in the 450 barrel. In your experiment, did you have to put the brass piece back after each shot? or did it eject with the spent 9X19 Casing? The other issue I am thinking about is the bolt. If 45 acp AR15 bolts are anything like my 9mm bolt, I wonder if the regular bolt carrier will be heavy enough for blowback operation versus gas? |
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I think at a minimum you need a chamber adapter, a blowback .45 ACP bolt, and a lower set up for some kind of .45 ACP mag. A machinist might be able to make you a chamber adapter, I don't know how you get it back out of your barrel once it carbon locks. For the money, you're better off just purchasing a complete .45 ACP upper, magwell adapter, & mags from Rudy - or get one of the ASR ARish .45 ACP carbines that run Glock or 1911 mags. |
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Not a strange idea in the least, some guy named Pedersen had a similar idea and sold a ton of them to Uncle Sam... but they never were fielded because WWI ended... And there are 22LR adapters that go in a .223 chamber to do the same thing. The 45 ACP would be blowback, and use a blowback bolt, which generally place the chamber further backwards as you are not locking bolt lugs into extension lugs. So your adapter would be flush with the extension 'face'. Extracting the adapter would be the challenge, as has been noted. That said, you could try pushing it out with a cleaning rod from the muzzle... Swapping uppers is faster... |
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"You got out once. You dip so much as a pinky back into this (ARFCOM) pond... you may well find something reaches out... and drags you back into its depths".
"You got out once. You dip so much as a pinky back into this (ARFCOM) pond... you may well find something reaches out... and drags you back into its depths".
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Originally Posted By MartytW: Not a strange idea in the least, some guy named Pedersen had a similar idea and sold a ton of them to Uncle Sam... but they never were fielded because WWI ended... And there are 22LR adapters that go in a .223 chamber to do the same thing. The 45 ACP would be blowback, and use a blowback bolt, which generally place the chamber further backwards as you are not locking bolt lugs into extension lugs. So your adapter would be flush with the extension 'face'. Extracting the adapter would be the challenge, as has been noted. That said, you could try pushing it out with a cleaning rod from the muzzle... Swapping uppers is faster... If you had a controlled feed bolt might not have to have a chamber insert.....but not sure how long the bushmaster chamber would survive  ..... Damn Marty....how ya been, long time since I've seen you around.............give me a shout at the shop sometime.....or a call if you still have my cell number.....
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Originally Posted By Mad-Machinist: If you had a controlled feed bolt might not have to have a chamber insert.....but not sure how long the bushmaster chamber would survive ..... Damn Marty....how ya been, long time since I've seen you around.............give me a shout at the shop sometime.....or a call if you still have my cell number.....Yeah, work had some other plans for me a few years ago... so much for 'short term assignment'... slowly getting back into it. Send me a DM! On the original topic: You'd definitely want / need the insert because the 450 BM case is larger diameter than the 45 ACP. Talk about an unsupported chamber It can be done, I mean, we sleeved a 7.62 Tok chamber and barrel into a 9mm PT92 barrel... similar concept, the Tok barrel rests on the 'ledge' where the 9mm case headspaces... barrel is threaded and uses a collar to tension it against the end of the original barrel. But I digress. Due to the super short gas system on the 45 ACP DI, it suggests that blowback is really the only option for this insert. That moves the mouth of the chamber back like on the Colt pattern 9mm barrels. This means you can make the insert rest on the 'ledge' around the outside of the 450 BM chamber and the ID of the barrel extension. The insert into the chamber itself could then be slightly undersize, making later removal a bit easier potentially. But again, swapping uppers is so easy and you can build one for very little these days in you shop around. You need the receiver ($50 if you look around), hand guard (as low as $30 if you want to go cheap) and a barrel... Steal a charging handle from another upper. I guess the bolt, but you would need that for your insert version as well, so that is a 'wash'. |
Be careful when the boss asks "Have you ever been to ...?"
"You got out once. You dip so much as a pinky back into this (ARFCOM) pond... you may well find something reaches out... and drags you back into its depths".
"You got out once. You dip so much as a pinky back into this (ARFCOM) pond... you may well find something reaches out... and drags you back into its depths".
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Originally Posted By txsgar15a2: That is kind of how I see that happening with the 450 to 45 conversion. I don't need for the gas tube to work as 45 is blowback anyway. I am thinking on the idea you used in the Destroyer Cabine. That would definitely allow the .45 acp cartridge to head space correctly in the 450 barrel. In your experiment, did you have to put the brass piece back after each shot? or did it eject with the spent 9X19 Casing? The other issue I am thinking about is the bolt. If 45 acp AR15 bolts are anything like my 9mm bolt, I wonder if the regular bolt carrier will be heavy enough for blowback operation versus gas? But if your going to rely on blowback, the bolt must remain unlocked and not lock as it normally does in gas tube systems, right? Which also means you need a different bolt design. It's not just the weight of the blowback bolts. It's also that they typical don't have the cam pin and the lugs on the bolt that lock it in place. So, it would seem to me you are gonna need a gas tube and you're gonna need some way to adjust that to work with both different cartridges. One idea might be to have a barrel with 2 different gas ports at 2 different locations and different sizes. Of course you'd need 2 gas ports and somehow tee the 2 together. You'd also probably need those gas blocks to have some sort of valve to turn them on and off to switch back and forth. It might be doable, but would add complexity and you'd have to remember to make the adjustments to the gas blocks when switching back and forth. |
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