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Posted: 7/26/2026 7:44:38 PM EDT
| I have ran hand tightened benchrest rifle barrels in the past. I have the same idea with a cmmg 9mm RDB. Torque the barrel nut as usual 30-80 and thread the barrel in by hand. There is no gas tube to align and install. As long as the barrel is kept tight, would this be safe in a BCA bolt action or single shot straight pull set up using a 5.45x39 bolt? I guess it would be like a DIY backpack/breakdown SBR AR15 in 9mm. |
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Why though? You still have a good length of handguard sticking out from the receiver. Also, the bolt rotates counterclockwise when unlocking (looking at it from the bolt face). Frictional forces by the bolt on the obturated case in the chamber during cycling are going to be in the direction of loosening a RH threaded barrel/extension. |
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FWIW, when a barrel extension is torqued down on a barrel (150 ft/lbs), it tries to collapse the chamber a bit. I could see in a benchrest environment, that inducing a bunch of stress may not be good. You may be better off using very little torque on the extension and gluing it in place with Loctite. Tony |
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Originally Posted By TonyRumore: FWIW, when a barrel extension is torqued down on a barrel (150 ft/lbs), it tries to collapse the chamber a bit. I could see in a benchrest environment, that inducing a bunch of stress may not be good. You may be better off using very little torque on the extension and gluing it in place with Loctite. Tony It’s like asking what mods are going to let your Toyota Corolla run competitively in the Le Mans race… at some point you’re better off using a different platform more suited to the end goals (than pistol caliber AR or bottom tier bolt-AR). There are a few legitimately take-down centerfire bolt guns out there, but they’re usually not cheap. I would actually investigate Ruger American Ranch rifles with both a folding chassis and a hand-tight short barrel (stamps are free!). You could probably get a RAR in 300BLK or .338ARC down to backpack or briefcase stowable — and it would certainly outperform an AR based platform in accuracy, reliability, quietness and quality. |
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Originally Posted By CROWMINATOR: I am planning on using an old school round hand guard, that can be threaded on and off without having to line it back up with anything. Haha! I actually have a BCA bolt action upper receiver with an old school YHM round handguard and a BA .300BLK 10” barrel. I use it with one of my random SBR lowers and It’s super quiet with a Q titanium can and a ton of fun. It’s accurate enough… maybe 1-2” MOA. Which is fine considering its provenance is just a BCA upper and BA barrel and it’s limited to .300BLK ranges. |
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I'm having trouble understanding the OP. Are you asking for a benchrest gun or a gun that you can break down? Or both? There is a way to have a breakdown kit for the AR15. I think it is called a cry havoc system or something to that effect. It lets you take the barrel off and be able to put it back together without problem. I would think the barrel extension idea sounds dangerous because how would you make sure the headspace is correct each time? Even being off a little could be deadly. |
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Originally Posted By dalle0001: I'm having trouble understanding the OP. Are you asking for a benchrest gun or a gun that you can break down? Or both? There is a way to have a breakdown kit for the AR15. I think it is called a cry havoc system or something to that effect. It lets you take the barrel off and be able to put it back together without problem. I would think the barrel extension idea sounds dangerous because how would you make sure the headspace is correct each time? Even being off a little could be deadly. I mentioned the hand tightened benchrest barrel because that is what I have done in the past. Wouldn’t the headspace be set every time the barrel is threaded back in until it stops in the shoulder ? |
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Originally Posted By CROWMINATOR: I mentioned the hand tightened benchrest barrel because that is what I have done in the past. Wouldn’t the headspace be set every time the barrel is threaded back in until it stops in the shoulder ? As far as I know when you get a barrel without the extension, the chamber hasn't been reamed yet since the headspace is unknown. I guess in theory if you get the extension, line it up exactly each time with the same amount of hand torque, it in theory would be set correctly each time? But perhaps I am wrong since I never did that project before. I remember my M1 Garand and M1a projects that I did off fulton armory, I recall after tightening the barrel, I had to lap the bolt until it closed on a go gauge but not close on a no go gauge. I would imagine anytime you have to screw a barrel in, for any sort of gun, you have to make sure the headspace is set correctly. I'm sort of not buying into this idea that you can screw a barrel into an extension and it would shoot fine by hand tightening it. That sounds.... dangerous to me. Personally I would like to see a video of you doing this. As an example the difference between a Go and Field gauge is only .0100 of an inch for a .223 round. That means if you hand tighten it and is off aby just a hundredth of an inch, you're in the danger category. |
| With the OP’s intended use, 9mm, no gas tube, etc, I’d consider hand tightening the barrel nut to the receiver versus a barrel to the extension. In addition, many handguards would prevent it from loosening. It would be easy to hit or get close to 30 ft lbs with hand tools in the field and it would probably be fine with less. The “up to 80” spec is only there for gas tube/barrel nut alignment. |
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Originally Posted By CROWMINATOR: I have ran hand tightened benchrest rifle barrels in the past. I have the same idea with a cmmg 9mm RDB. Torque the barrel nut as usual 30-80 and thread the barrel in by hand. There is no gas tube to align and install. As long as the barrel is kept tight, would this be safe in a BCA bolt action or single shot straight pull set up using a 5.45x39 bolt? I guess it would be like a DIY backpack/breakdown SBR AR15 in 9mm. In a 9mm AR there is no locking, so as long as the barrel cannot move, nothing bad will happen. That said. with an AR type design the barrel is cantilevered off the upper receiver, so a rigid connection is required for accuracy. |
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Originally Posted By CROWMINATOR:The dark mountain arms stowaway uses a tool less, hand tightened barrel nut. Just trying to figure out a way to safely replicate that with AR parts. |
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