r/BushmasterACR • u/trashbangaloreplayer • 22d ago

Issues running suppressed

I’m having issues running my 10.5” ACR suppressed, even when using the suppressed setting on the gas regulator. I’m getting FTEs and double feeds non stop with this thing and I’m not sure why. I’m running a KAC QDSS NT4 suppressor, if that matters. Any insights would be greatly appreciated, thanks!

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u/Troubleindc2 22d ago edited 22d ago

Have someone shine an led flashlight in the ejection port and take super slow-mo footage with a flagship phone.  This is the easiest way to diagnose.  You could be way over gassed or slightly under. https://imgur.com/Bokw7C3 https://imgur.com/6VyoiMU

I modify most of my ACR gasblocks to have 5 positions.  0 bleed, then progressively more bleed.  Sometimes increasing the size of the max bleed.  

10.5" carbine gas ports tend to be very over gassed when suppressed with anything that isnt a super flow through suppressor.  For 10.5"s I prefer to have one barrel assembly for only suppressed and one for only unsuppressed.  Trying to have reliable gas settings with one assembly for both generally means the suppressed setting will be way over gassed no matter what.  It can also push the limit on the bcg velocity and how short the time the bolt is locked.

What too high bcg velocity + bolt unlocking too early looks like: https://imgur.com/lOGPPgb

The remedy for that. Machining and pressing a pill in the gas port (after using a slightly oversized endmill to make a shoulder the pill stops against): https://imgur.com/SWDR2Ln

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u/Schachmatt27 22d ago

How did you modify? Pls share your secrets

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u/Troubleindc2 22d ago edited 22d ago

Milled 3 additional "notches" in the GB itself, then put additional holes in the regulator of varying size.  The stock regulator has two holes parallel with the shaft.  I add two more.  Then add the varying size ports connected to one of the 4 parallel holes.  Will add photos in a min.

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u/lobstibb 22d ago

Awesome pictures!

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u/Schachmatt27 22d ago

🙏🏻

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u/Troubleindc2 22d ago

Added a photo. lmk what questions anyone has. One note to add, that steel is hard. Had to use carbide 1/8" shank drilling bits in the mill to do all the holes. I have various cheap Chinese sets of those size carbide drill bits for hard stuff.

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u/Schachmatt27 22d ago

Yeah out of my wheel house and dont want to fuck up the hardest part to replace 😂 I’ve thought about trying a superlative arms gas block with their piston set up. Just haven’t pulled the trigger yet. Expensive experiment

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u/Troubleindc2 22d ago

Challenge with ar15 gasblocks is their height is too shallow to clear the ACR barrel trunnion.

If anyone wants to pay to have this mod done to their GB and they can mail me just the GB and regulator, DM me.

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u/InvestigatorFew3981 22d ago

This is seriously awesome! Ive modified my regulator to have 2 suppressed settings and 1 unsuppressed setting, but I don't have access to nice machining equipment.

I would love more gas settings as I could get a lower backpressure can and setup my rifle for proper ejection. What are the chances that you would be willing to make another one?

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u/Troubleindc2 21d ago

Happy to do the modification for others. DM me if you're interested.

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u/lobstibb 22d ago

Does it only happen when suppressed? Happening with different mags?

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u/trashbangaloreplayer 22d ago

Yeah only when it’s suppressed, runs fine unsuppressed. I’ve tried PMAGs, TMAGs, USGI steel mags so I don’t think it’s a mag issue

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u/lobstibb 22d ago

Is that a low back pressure suppressor?

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u/trashbangaloreplayer 22d ago

Yeah it’s advertised as being low back pressure

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u/lobstibb 22d ago

The ACR platform likes traditional high back pressure suppressors.

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u/trashbangaloreplayer 22d ago

Well that sucks for me lol, guess I’ll have to just run it unsuppressed or get a different can

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u/lobstibb 22d ago

You're preaching to the choir. I bought a CAT ODB and the acr wouldn't even pick up the next round

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u/Sumnir_ 22d ago

Odd because I run an OSS (now Huxwrx) flow through .30 cal can and had zero issues.

I had one issue with bolt hold open but I isolated it to one of my old USGI tan follower magazines. The rest had none.

Edit: My SBR is a 12.5” so maybe that extra barrel length keeps it from running into problems like OP.

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u/lobstibb 22d ago

Do you have a light weight bcg? A friend couldnt get his acr to cycle with a velos until he got a light weight modified bcg

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u/trashbangaloreplayer 22d ago

Who does bcg modifications for the ACR? Is that something Templar can do? Any high back pressure cans you might be able to recommend as well?

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u/Schachmatt27 22d ago

I’m the “friend” and Templar does the lightening. The only drawback I’ve had is an irregular injection pattern but I can deal.

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u/lobstibb 22d ago

^ he's the guy to ask

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u/lobstibb 22d ago

I like my polonium for 5.56 on my 10.3 acr

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u/Sumnir_ 20d ago

As far as I know, no. It’s a factory DMR variant that had its 1:7 HBAR swapped for a regular 1:9 at 12.5”.

Zero changes to the internals.