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Posted: 9/9/2026 12:08:09 AM EDT
[Last Edit: PerfectTurn][Edited]
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Hey all, having some issues with a barrel fitting onto a receiver I’d like some help with. Long story short, about 5 years ago I bought a Colt M203 with a 37mm 9” barrel from Arms Unlimited. I also bought another Colt M203 bare receiver from Arms Unlimited. The 9” 37mm barrel works beautifully on both. Fast forward to last week… I bought a “Colt 12” 37mm Barrel” from Arms Unlimited with hopes of having both a 9” and 12” option for builds. Immediately after opening the box I was a little surprised at the glossy finish but didn’t think too much of that with all of the variations on 203 barrels. When I tried to install the barrel, the excitement ended… goes on about 1/4” and that’s it, it binds. I’ll post up dimensions and better pictures tomorrow but the only thing looking “off” right now in terms of fitment is this “step”. It appears it’s causing the bind. I’m going to email AU and ask if they’ve had any returns on these I guess? Not sure if someone swapped parts? There’s a lot of differences between these “Colt” 9” and 12” 37mm barrels, and I get it, different contractors, sub contractors etc etc, but something isn’t right, obviously. Do anyone know if the LMT 37mm barrels have this step? Thanks all! Attached File Attached File Attached File Attached File |
| I don't really have any real feedback as much as a data point for ya... I have three of the Colt 37mm units and the 9" and 12" 37mm Colt and 40mm LMT barrels swapped interchangeably, easily, between units before settling in final configs. My Colt receivers and barrels are all from an earlier batch, though, and shipped with the units. I would expect their Colt barrels to fit in Colt receivers, but I wouldn't past AU to sell "mislabeled" stuff. Its may be a longshot on the 37mm parts, but do either of your Colt barrels have a cage code? My LMT 40mm barrels do, but I need to dig for a 37mm before I can check. |
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Originally Posted By Ehtacs: I don't really have any real feedback as much as a data point for ya... I have three of the Colt 37mm units and the 9" and 12" 37mm Colt and 40mm LMT barrels swapped interchangeably, easily, between units before settling in final configs. My Colt receivers and barrels are all from an earlier batch, though, and shipped with the units. I would expect their Colt barrels to fit in Colt receivers, but I wouldn't past AU to sell "mislabeled" stuff. Its may be a longshot on the 37mm parts, but do either of your Colt barrels have a cage code? My LMT 40mm barrels do, but I need to dig for a 37mm before I can check. Thanks for the reply! No cage code on either except for the plastic handguard 12012007. I just really don’t think this 12” 37mm “Colt” from AU is milspec for an M203 at all. It’s several thousandths off, not even close to “it’ll wear in” I emailed AU today to see if any of these “Colt 12” 37mm barrels” were returned. Maybe a buyer swapped in something else for the return? I wish I could see the LMT 37mm rail/interface because supposedly that is a different animal than milspec. |
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Originally Posted By Gingerbreadman: I thought that there was a factory 37mm M203 that wasn't compatible with 40mm barrels. No idea where I read that though. LMT and only LMT made one. It had a different model number and was not considered a firearms so it could ship directly to you |
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