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Posted: 4/5/2026 8:14:45 AM EDT
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Need some help/opinions/suggestions. Rifle in question is a older DPMS made back during the ban. It had no bayo lug. a unthreaded muzzle, and the neutered (unshrouded) BCG. It is a standard 20 inch A2 style rifle, with a flat top upper (A4?). 1-9 twist chrome lined bore/chamber. When I bought it at a gunshow for $450, it was my plan to make it my dedicated FRT rifle. It had what appeared to be a cheap china carbine buffer tube and stock on it. Since I had a spare A2 stock, I ordered a standard A2 rifle length buffer tube and buffer. I went ahead and got a tubbs flat wire buffer spring for it, since I was ordering a spring. I bought a toolcraft standard/FA BCG. I removed the barrel and threaded the muzzle, but did no other mods to the barrel. Still has the factory non bayo lug FSB and gas tube.  I bought a ASD ARC-fire and had them cut a G2S trigger for it. For a while it was great, ran perfectly. I put probably 300-400 rounds through it. I hated the small smooth selectors the arc-fire came with, and when they released the mil-spec style selectors, I bought then and swapped them on. That is when the issues started. It instantly became unreliable. I could only get 1-3 rounds before it stopped. Trigger was dead, hammer was down, live round in the chamber. I swapped the old selector back on and it went back to running. I assumed it was the new selector. I contacted ASD customer support, they sent me a new shaft, that did not fix the issue. They then sent me new selectors, that did not fix it. I then put all the original parts back in and it still refused to run. I thought the trigger my have been cut wrong, so I cut a new trigger and it made no change. I figure now is the time to see if the issue stays with the trigger, or stays with the gun. I take the original trigger, and the new selectors and swap them into my DPMS G2 308. I then take a rare breed 3 pos that works fine in a different gun, and swap it into the A2. Results: The G2 308 runs fine with the arc-fire and G2S trigger. The A2 will not run with the RB either, it has the EXACT same issue. Stops anywhere between 1-3 rounds. Dead trigger, hammer down on a live round. I did get a couple times where I got almost half the mag before it stopped. But usually it was 1-3 rounds before it stopped. So since the issue stayed with the gun, I am thinking there is something wrong with the gun. But what? Bolt bounce, with a rifle buffer? Looking for any ideas or suggestions. Gun runs perfectly fine in semi auto. You can run it as fast as you can pull the trigger and it never misses a beat, locks open on a empty mag every time. When it stops during FRT, the round in the chamber does not have a light strike. It simply has that tiny mark from the firing pin that you get from simply chambering a round. I took a round, put it in the chamber, closed the bolt and then ejected it. I then compared it to one from when it stopped running in FRT and the marks are identical. Yes I know about the FRT forum, and yes I have a thread in there about it, but that was when I was focused on the FRT portion of it, thinking the issue was the FRT. Now that I found it issue stays with the gun, even with a different FRT, that makes me think there is a issue with the gun and not the trigger. Hence this thread trying to diagnose the gun. |
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I would check the weight of the sliding weight assembly in the rifle buffer. I've seen some with aluminum weights/spacers inside. They usually only have about 3.5oz sliding, which is a bit on the light side for stopping bolt bounce. I prefer 4oz or more. But, you are correct. Rifle buffers usually don't have problems with carrier bounce. Tony |
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I have no experience with any FRT, concerning the total of your troubleshooting I would look at a couple of things. I offer this just to see, and what it takes to fix it, please let us know what was failing and your fix when you get it running with your choice of FRT. Try maybe a Geissele braided rifle spring instead of the flat wire for a starter. Look at trigger. |
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Quoted: I would check the weight of the sliding weight assembly in the rifle buffer. I've seen some with aluminum weights/spacers inside. They usually only have about 3.5oz sliding, which is a bit on the light side for stopping bolt bounce. I prefer 4oz or more. But, you are correct. Rifle buffers usually don't have problems with carrier bounce. Tony I just weighed it and it is 5.5 ounces. |
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Quoted: I would try changing the flat wire spring out for a standard spring and check the buffer as mentioned above. I got digging around in my parts stash as I thought I had a standard rifle spring, but I do not. I have a wolff XP rifle spring, but not a standard rifle spring. I'll have to order a spring to be able to try one. |
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So a little update (kind of). I ended up getting pissed off at this rifle and used the lower to build a 9x23 carbine. I just tossed the upper in the closet for now. I bought a older bushmaster that is basically identical to this DPMS. It is all original other than me swapping the bolt carrier for a FA one. I installed a arc-fire V2 and a freshly cut $G trigger. It rips, runs perfectly in FRT. So I take and install the DPMS upper onto the bushmaster lower and it chokes, just the same as before. Hammer down, live round in the chamber, dead trigger. So seems the issue is in the upper. I tried swapping the BCG out of the DPMS upper into the bushmaster upper, and it ran perfectly on FRT. So the issue is not the BCG, it seems to be the upper (barrel/gas system) The DPMS upper does shoot noticeably softer than the bushmaster one. So could the DPMS upper be under gassed? |
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