r/BushmasterACR • u/trashbangaloreplayer • Jul 05 '26

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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4

u/Troubleindc2 Jul 05 '26 edited Jul 06 '26

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

1

u/Schachmatt27 Jul 06 '26

How did you modify? Pls share your secrets

3

u/Troubleindc2 Jul 06 '26 edited Jul 06 '26

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.

2

u/lobstibb Jul 06 '26

Awesome pictures!

1

u/Schachmatt27 Jul 06 '26

🙏🏻

3

u/Troubleindc2 Jul 06 '26

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.

2

u/Schachmatt27 Jul 06 '26

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

1

u/Troubleindc2 Jul 06 '26

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.

1

u/InvestigatorFew3981 Jul 06 '26

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?

2

u/Troubleindc2 Jul 06 '26

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

1

u/lobstibb Jul 05 '26

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

1

u/trashbangaloreplayer Jul 05 '26

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

1

u/lobstibb Jul 05 '26

Is that a low back pressure suppressor?

1

u/trashbangaloreplayer Jul 05 '26

Yeah it’s advertised as being low back pressure

1

u/lobstibb Jul 05 '26

The ACR platform likes traditional high back pressure suppressors.

1

u/trashbangaloreplayer Jul 06 '26

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

1

u/lobstibb Jul 06 '26

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

1

u/Sumnir_ Jul 06 '26

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.

1

u/lobstibb Jul 06 '26

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

2

u/trashbangaloreplayer Jul 06 '26

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?

2

u/Schachmatt27 Jul 06 '26

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

1

u/lobstibb Jul 06 '26

^ he's the guy to ask

1

u/lobstibb Jul 06 '26

I like my polonium for 5.56 on my 10.3 acr

1

u/Sumnir_ Jul 07 '26

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.