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Posted: 7/30/2026 8:51:51 AM EDT
| I have a CMMG 4.5 in upper for my SBR . What parts or kit is needed to get it to run with my ARC fire FRT? |
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You’ll probably need a bore buddy adjustable weight as well as a super safety sled/trip. I found there was too much slop between my GMR lever and cam that was causing issues. I replaced the lever with a 10% larger (printed) lever for a tight fit in the cam. That resolved the operating issues. Also used a Taylor Tactical low power hammer spring. |
| Order the Bore Buddy trip kit for the ArcFire, it will include the spacer for retiming as needed. |
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I can see where you're coming from, 'cause I know where you've been and I can see where you're going 'cause I can see the direction you're headed in. I just don't know where the hell you're at right now.
I can see where you're coming from, 'cause I know where you've been and I can see where you're going 'cause I can see the direction you're headed in. I just don't know where the hell you're at right now.
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I don't know how familiar you are with FRTs in general, but be prepared to do a LOT of troubleshooting and experimentation. There's a reason that Bore Buddy kit comes with a wide range of adjustable weights, and four different recoil springs, and a couple extractor springs. You will have to try a bunch of different combinations until you find the one that works best. I've found that the CMMG conversions are pickier than dedicated Bore Buddy uppers, so just be ready. While testing, ensure that you're regularly cleaning and lubing the conversion group. It sucks to get skewed data on a particular spring/weight combination because you're trying it after 500 rounds and it's gunked up. |
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I have a CMMG kit with a 16 inch dedicated .22 barrel. After much experimentation, I ended up going to an Atrius selector with the Rise 140 trigger for the lower, along with a buffer plug. The CMMG kit has the appropriate bore buddy trip, and weight sled with full weights, stock recoil spring, along with the super safety firing pin. With a suppressor it runs mini mags and aguila 100%. Other ammo is more finicky but that's to be expected, so I stick with those 2. It's a learning curve and there is no guaranteed combo. However in my experience the atrius and rise 140 are a big contributor to reliability so I'd recommend those if you haven't already started messing with other options. |
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