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Posted: 7/19/2026 4:02:17 PM EDT
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Okay, so I'm considering doing a M231 build and have gone down the rabbit hole. I may end doing an article on the history and a section on clone builds at some point. There doesn't seem to be a lot of documentation on them. Here's some stuff I was wondering about if anyone knows the answers. Also, if anyone actually used them in the service I'd love to hear any first hand experiences. 1. Any current source for the barrel collar? Looks like the H&R DOE handguards would work but I'd still need a barrel collar. 2. How does the barrel collar attach to the barrel or gas block? I see reference in the manual to a set screw. 3. Is it basically a low profile gas block under the collar? 4. Any source uppers? (I'm guessing no, I just asked Mayhem Machine about the possibility of doing some) 5. Any pics anyone has of originals, clones etc. would be awesome. Any help would be greatly appreciated! |
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I can't find my old pictures. At one point I nearly had all the parts to a M231 and was starting to make CAD drawings, but no one seemed interested and I ended up selling them to work on other projects. The M231 gas tube attaches or is part of a block. There is some sort of o-ring connector that goes between the barrel and this block, like a brass washer, spacer of sorts. The larger handguard retainer/weapon port threaded mount slides over that. |
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Originally Posted By tstetz: Okay, so I'm considering doing a M231 build and have gone down the rabbit hole. I may end doing an article on the history and a section on clone builds at some point. There doesn't seem to be a lot of documentation on them. Here's some stuff I was wondering about if anyone knows the answers. Also, if anyone actually used them in the service I'd love to hear any first hand experiences. 1. Any current source for the barrel collar? Looks like the H&R DOE handguards would work but I'd still need a barrel collar. No one currently makes/sells the collar. The DOE handguard is used on the M231. 2. How does the barrel collar attach to the barrel or gas block? I see reference in the manual to a set screw. The collar attached with a big set screw on the bottom and side two pins. 3. Is it basically a low profile gas block under the collar? The gas block is attached to the gas tube (see response #1) 4. Any source uppers? (I'm guessing no, I just asked Mayhem Machine about the possibility of doing some) Uppers dried up a long time ago. 5. Any pics anyone has of originals, clones etc. would be awesome. I have some clone photos I downloaded in 2019. Any help would be greatly appreciated! |
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Originally Posted By 57Octane: I wonder what thread pitch is on the gas block and how much of a pain it would be to turn  I see the humor but It’s been done before and can be again. I’ll try if I can get a one to copy. Like a barrel assembly not just a spec. Why. I won’t be able to actually tell you if it fits n works. |
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Don't forget to brush your teeth.
Don't forget to brush your teeth.
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Y'all work too hard.... Why repro 'em when you can buy my repros? Attached File Original or repro? you tell me: Attached File The pins on the bottom are not standard 2/0 FSB pins, they're #2 taper pins, quite a bit larger. I had my repro's made with no pilot holes so if you want to pin it to your barrel like OE, you don't have to try to line up on the prior taper hole locations and then machine the barrel in a weird oblique unsupported angle. With mine, you indicate off the hole and machine barrel and collar together, just like Colt did. Or hit the Easy button and just used the set screw. You're not going to shoot it that much anyway. 
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Originally Posted By Dex223: Okay, so I'm considering doing a M231 build and have gone down the rabbit hole. I may end doing an article on the history and a section on clone builds at some point. There doesn't seem to be a lot of documentation on them. Here's some stuff I was wondering about if anyone knows the answers. Also, if anyone actually used them in the service I'd love to hear any first hand experiences. 1. Any current source for the barrel collar? Looks like the H&R DOE handguards would work but I'd still need a barrel collar. No one currently makes/sells the collar. Ahem, I do. 2. How does the barrel collar attach to the barrel or gas block? I see reference in the manual to a set screw. The collar attached with a big set screw on the bottom and side two pins. 3. Is it basically a low profile gas block under the collar? The gas block is attached to the gas tube (see response #1) Yes, and the gas port is in the standard Carbine location on the barrel. 4. Any source uppers? (I'm guessing no, I just asked Mayhem Machine about the possibility of doing some) Uppers dried up a long time ago. 5. Any pics anyone has of originals, clones etc. would be awesome. I have some clone photos I downloaded in 2019. Any help would be greatly appreciated! |
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Originally Posted By Dex223: Like I posted previously, I believe these are from a replica/clone build, but the parts are similar to the real thing. Collar https://i.imgur.com/xSeRoWA.jpg Where it attaches to the barrel https://i.imgur.com/fXwyJUd.jpg The gas port/bushing recess https://i.imgur.com/Lb9RGRR.jpg Bushing in the barrel https://i.imgur.com/OqgXE3L.jpg Gas block with attached gas tube https://i.imgur.com/3jghJZm.jpg That gas key is not original (although aside from material, looks accurate). It looks like someone shaped it on a sander? The originals were grey parkerized like the collar, and machined, not sanded/ground. |
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Originally Posted By cmeyer001: so, being that the 231 was an open bolt design, how you going to address that? Bolt carrier and all the lower internals are quite a bit different. That's not something I'm trying to replicate. I don't even think you're allowed to do open bolt semis any more even if I wanted to. I'm mainly looking at getting the external details as close as I reasonably can. I'll use a conventional BCG and FCG, and am going to try a Hoffman Trigger Kicker FRT if and when it all comes together. |
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Originally Posted By cmeyer001: so, being that the 231 was an open bolt design, how you going to address that? Bolt carrier and all the lower internals are quite a bit different. I haven’t fired an open bolt M16 yet. All my stuff is regular style. The more I think about it the more it scares me. And why?? It could blow up the TM even has warnings about swapping parts from other guns I know what the auto sear is gonna do it’s predictable. |
It's not paranoia if there really is somebody after you
Don't forget to brush your teeth.
Don't forget to brush your teeth.
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Originally Posted By M-231: Is there an FRT that works with a drop-in trigger pack? If so, John Thomas had the absolutely brilliant idea to only drill the trigger pin (assuming using an 80%), and use only the trigger pin to retain the drop-in trigger, thus preserving the external look. Not that I'm aware of. |
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If using a cassette style FRT, I would think you could secure it forward with a screw forward of the trigger, up through the bottom of the lower to hold it. Or perhaps a metal insert to hold the fire control group like they do on the 3d printed MP5 grip housings to hold AR parts. Either way, there are other holes in the lower on the M231 that I'm not sure you'd want to drill.  
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