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Posted: 11/27/2023 12:38:32 PM EDT
[Last Edit: DocApocalypse]
I love my CMMG 22lr conversion unit for the AR-15.. Since I have two identical Colt 6920's set up the same, I wanted to leave the Bravo conversion kit in one of them all the time. But the instructions say not to do so.
What is the reason for this? |
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Posted: 11/27/2023 6:17:21 PM EDT
[#1]
Probably to insure that any corrosion doesn't lock it in place or damage the chamber.
That chamber insert is pretty thin and it wouldn't take much to damage it |
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Posted: 11/27/2023 6:30:29 PM EDT
[#2]
Originally Posted By DocApocalypse: I love my CMMG 22lr conversion unit for the AR-15.. Since I have two identical Colt 6920's set up the same, I wanted to leave the Bravo conversion kit in one of them all the time. But the instructions say not to do so. What is the reason for this? Lead builds up in the FSB and gas tube. If you subsequently. fire a few centerfire cartridges through the barrel, it'll eventually blow out and clean up any leading. But it might also not cycle properly if the build-up is too great. Dedicated .22 uppers don't need a gas tube, and probably come (or can be built) with a faster 1/12 or 1/16 twist rate barrel that provide better accuracy with typical .22LR ammunition. |
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Posted: 11/27/2023 6:31:47 PM EDT
[#3]
Quote HistoryOriginally Posted By GunnyG: Lead builds up in the FSB and gas tube. If you subsequently. fire a few centerfire cartridges through the barrel, it'll eventually blow out and clean up any leading. But it might also not cycle properly if the build-up is too great. Dedicated .22 uppers don't need a gas tube, and probably come (or can be built) with a faster 1/12 or 1/16 twist rate barrel that provide better accuracy with typical .22LR ammunition. Quote HistoryOriginally Posted By GunnyG: Originally Posted By DocApocalypse: I love my CMMG 22lr conversion unit for the AR-15.. Since I have two identical Colt 6920's set up the same, I wanted to leave the Bravo conversion kit in one of them all the time. But the instructions say not to do so. What is the reason for this? Lead builds up in the FSB and gas tube. If you subsequently. fire a few centerfire cartridges through the barrel, it'll eventually blow out and clean up any leading. But it might also not cycle properly if the build-up is too great. Dedicated .22 uppers don't need a gas tube, and probably come (or can be built) with a faster 1/12 or 1/16 twist rate barrel that provide better accuracy with typical .22LR ammunition. I plan to stick to jacketed ammo. Will this mitigate any lead buildup? |
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Posted: 11/27/2023 6:33:48 PM EDT
[#4]
Quote HistoryOriginally Posted By jos51700: Probably to insure that any corrosion doesn't lock it in place or damage the chamber. That chamber insert is pretty thin and it wouldn't take much to damage it Less likely to happen than lead building up, I 've been using Fluid Film to lube the chamber insert for years, but an antiseize compound would work too. |
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FL, USA
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Posted: 11/27/2023 6:39:04 PM EDT
[#5]
From a safety standpoint, I always swapped in a standard BCG and fired a few 5.56 rounds at the end of every range session just to be sure. Really cheap insurance to keep the rifle fully functional.
Accuracy with the drop in conversion was always suboptimal for me. Doesn't CMMG sell a barrel that replaces the chamber adapter? If you don't plan on shooting 5.56 in that rifle anymore, you could probably sell the barrel/BCG combo on the EE and fund a dedicated barrel in .22lr. |
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OK, USA
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Posted: 11/27/2023 6:45:09 PM EDT
[#6]
Quote HistoryOriginally Posted By GunnyG: Lead builds up in the FSB and gas tube. If you subsequently. fire a few centerfire cartridges through the barrel, it'll eventually blow out and clean up any leading. But it might also not cycle properly if the build-up is too great. Dedicated .22 uppers don't need a gas tube, and probably come (or can be built) with a faster 1/12 or 1/16 twist rate barrel that provide better accuracy with typical .22LR ammunition. |
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Posted: 11/27/2023 6:47:30 PM EDT
[#7]
Quote HistoryOriginally Posted By DocApocalypse: I plan to stick to jacketed ammo. Will this mitigate any lead buildup? Yeah, you should be good to go for cleaning up the bore. The gas system is what will need the higher gas pressures generated by centerfire cartridges to potentially clear any fouling in the FSB and gas tube. How frequently that can happen is going to be the issue. When I'm using a .22 conversion, I'm probably also on an indoor pistol range , and they tend to frown on using any centerfire rifle ammo, for obvious reasons. That's why I built an upper dedicated to .22LR |
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Posted: 11/27/2023 7:04:58 PM EDT
[#8]
Quote HistoryOriginally Posted By GunnyG: Yeah, you should be good to go for cleaning up the bore. The gas system is what will need the higher gas pressures generated by centerfire cartridges to potentially clear any fouling in the FSB and gas tube. How frequently that can happen is going to be the issue. When I'm using a .22 conversion, I'm probably also on an indoor pistol range , and they tend to frown on using any centerfire rifle ammo, for obvious reasons. That's why I built an upper dedicated to .22LR Quote HistoryOriginally Posted By GunnyG: Originally Posted By DocApocalypse: I plan to stick to jacketed ammo. Will this mitigate any lead buildup? Yeah, you should be good to go for cleaning up the bore. The gas system is what will need the higher gas pressures generated by centerfire cartridges to potentially clear any fouling in the FSB and gas tube. How frequently that can happen is going to be the issue. When I'm using a .22 conversion, I'm probably also on an indoor pistol range , and they tend to frown on using any centerfire rifle ammo, for obvious reasons. That's why I built an upper dedicated to .22LR Even though the instructions say to "clean it out" by firing 5.56 after using the adapter, this Brownells video says that is a bad idea. So, even this is controversial.  Brownells - Cleaning the Brownells CMMG AR-15 .22 Conversion Kit |
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MI, USA
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Posted: 1/8/2024 11:30:55 AM EDT
[#9]
Quote HistoryOriginally Posted By jos51700: Probably to insure that any corrosion doesn't lock it in place or damage the chamber. That chamber insert is pretty thin and it wouldn't take much to damage it The first CMMG (and other brand) .22 conversions were phosphate ("parkerized") coated carbon steel, and could indeed become corroded into the chamber. Stainless steel as an option from CMMG came later, and eventually became all that is sold by CMMG. MHO, YMMV, etc. |
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Posted: 1/8/2024 11:38:14 AM EDT
[#10]
Quote HistoryOriginally Posted By SecondAmend: The first CMMG (and other brand) .22 conversions were phosphate ("parkerized") coated carbon steel, and could indeed become corroded into the chamber. I'm thinking this would never be an issue in chrome-lined barrel, would it? |
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