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Discussion Starter · #1 ·
I recently bought an ACR with a 16 inch barrel, shot 60 rounds thru it but decided I wanted to go with a shorter barrel and purchased a 14.5 inch Remington defense barrel and now my gun will not cycle. I presume this is an issue with the gas system as the ACR is notorious for it (I also took it apart to make sure everything was assembled correctly and it was), does anyone know what I need to do to fix this problem?
 

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I wonder if the gas port on the barrel is obstructed. Try removing the gas block. Also, if you have drill bits or pin gauges, you can see what the port diameter is. And finally, are you shooting the rifle with the gas selector set to suppressed or unsuppressed? What type of ammo?

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Discussion Starter · #5 ·
I took it apart and didn’t find anything, I even took apart my 16 inch barrel to see if I was missing something, everything looks fine, and the rifle shoots and cycles fine with the 16 inch barrel
 

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There's either not enough gas moving out of the barrel's gas port to actuate the piston, thus moving the BCG backwards, or something is binding severely enough to prevent movement. Hard to tell unless I'm physically looking at the rifle.

Are you sure the regulator knob is in the correct position? Compare the regulator assembly between the two barrels. Is there anything different about the newer one?



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Pictures won't really help. Would need to check the gas port with pin gauges to make sure it's the right diameter and not undersized. I'd also have to check the gas block to make sure it's properly drilled out and centered over the gas port. Finally, would need to check that the piston assembly isn't binding and that it travels freely once the barrel is locked into the trunnion.

Only thing I can suggest is for you to take it to a reputable smith or someone with a good understanding of how a piston gun operates and have them look over everything. If you have a buddy with another ACR, you could also try your barrel in their receiver in order to eliminate variables. If it works in another ACR, then there's something amiss with your particular configuration, likely from tolerance stacking during manufacturing.

Out of curiosity, but where did you source the barrel from and are you sure it's a Remington Defense unit?

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My guess is the barrel gas port is the wrong size. I received a brand new match grade barrel for a rifle build which had a similar issue. Took it to a reputable gunsmith and he checked the port size with some pin gauges. Turns out the factory messed up and used a far too small drill for the port size and caliber.

I’m not sure what the correct size would be You may be able to find it on the forum. But a good gunsmith would know.

Best of luck to you getting your rifle up and running.
 

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Would you mind texting me at this number? I will send you pics, I see no difference at all and yes I have it in the correct Unsuppressed mode
have you tried firing it on both Unsuppressed and Suppressed? I ask because I had the same issue and while at the range recently, it dawned on me to try both modes. I switched it to suppressed and it worked. Long story short, I put the regulator in backwards when I reassembled the barrel after a deep clean. Unsuppressed = Suppressed and Suppressed = Unsuppressed with it being backwards. Worked just fine after I sorted myself out haha
 

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I recently bought an ACR with a 16 inch barrel, shot 60 rounds thru it but decided I wanted to go with a shorter barrel and purchased a 14.5 inch Remington defense barrel and now my gun will not cycle. I presume this is an issue with the gas system as the ACR is notorious for it (I also took it apart to make sure everything was assembled correctly and it was), does anyone know what I need to do to fix this problem?
Had a very similar situation with a barrel. The op rod guide was just slightly off center. Hard to tell at a glance but it was binding the op rod enough that it would not properly cycle. It is an easy check and easy fix.
 

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I recently bought an ACR with a 16 inch barrel, shot 60 rounds thru it but decided I wanted to go with a shorter barrel and purchased a 14.5 inch Remington defense barrel and now my gun will not cycle. I presume this is an issue with the gas system as the ACR is notorious for it (I also took it apart to make sure everything was assembled correctly and it was), does anyone know what I need to do to fix this problem?
So, the RemDef barrel. I own a number of them and Remdef had a huge quality control issue. I myself SBRd one of my ACRs that is a complete Remdef build and I had the same issue with the 10.5 I installed. The Remdef barrels seemed to almost always have really small gas ports on the regulator plug. My particular problem was short cycling. I took a 5/64 drill bit and drilled into the port hole to allow more gas to flow through and was fine after that. Also, if the piston op rod is crooked even in the slightest way, it can also cause these issues.
 
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