I purchased a barely-fired DMR ACR for something approaching highway robbery. I then sold the stock and barrel and picked up a folding stock and two 16” 5.56 M4 barrels with the 1-9” twist. I got it to the range today and ran it suppressed like I was mad at it. everything worked flawlessly. I’m thinking that now I want to SBR this ACR. I have an extra barrel. Should I send an M4-cut barrel somewhere to be cut and threaded or should I drop $450 (on sale) for a new barrel? I’d really rather not buy a whole new barrel.

Any reason not to just cut a barrel to 11-12”? Any ideas where I can send this barrel unit to be cut and threaded? Thanks.

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I honestly like the 1/9 barrels.  With that being said the cheapest options you have is to either cut it down or reuse the parts on a custom build using a barrel of your choice.  New barrels are nice because it’s out of the box ready to go but aftermarket is the way to go if you want performance.

This is a range toy. The 1/9 barrels work just fine for me. I’m just wondering if the gas port in the barrel or gas block will be sized incorrectly and give me reliability issues if I take 4-5” off the barrel.

Anybody who can cut down the barrel should be able to re-port. I vote to cut and retain the 1:9.

Ive been told by multiple smiths that the ACR does not need a new port job once chopped.  so youll just need to get a chop and thread job.

ETA:  My barrel is off getting chopped and dimpled to 12.5"(about as short as you can get and keep the factory 'mid length' gas block).

And ill definitely be buying a 8-10" 300BO set up to swap in when they come out.

This is very helpful. Thanks!

Now, where should I send it to get chopped? What’s the cost? Do I also need to remove the gas block and piston assembly before sending it in?

ETA: ADCO charges $140

Class 3 Machining did my ACR cut and thread for $90 with a one week turnaround. He’s done many barrels for me and it’s always good price and fast turnaround time. The work is excellent too. I think if you want a flash hider pinned and welded he charges 20 bucks etc or something.
Once I got my barrel down to 14.5 it fealt a lot lighter up frond
He is also a vendor here with a page in the industry section

Thank you, Turrican. I found him in the vendor forum and sent an email. He has great feedback from other members here.

I, too, have used C3 for a barrel chop on my FAL.  Even did it in the weird factory FAL pitch.  Coincidentally, the gas port on the FAL does not need to be opened up either.

The gas system on FALs is wholly different than the ACR, but the ACR gas plug is very similar.  That's a cool feature.

Anyway, when I sent my barrel out for chop, I stripped it down to the gas block.  The gas block at its largest dimension is 1 5/6", so it should fit in past the chuck on any decent lathe.  I didn't worry about taking it off, as it would have been a PITA.  I did strip it the rest of the way.  The piston and spring parts disassemble pretty easy for it not to be a hassle.

Also, since I left the gas block on, I had to leave the barrel wrench on.  I'm sure when getting chopped it will get taped down or something to keep it from hinging open while spinning in the lathe.

Lastly, if you're in Utah, I know a guy that does this kind of stuff if you want it done in person.  If not, i'd say send it out.  C3 was pretty quick.

I will with a 100% certainty say you will have to open your gas port unless you only run suppressed. Even a 14.5” barrel needs the port opened up.

I mean you could always just remove mass from the carrier as an alternative to opening the port size. Though the port is probably the easier solution of the two

I will only be running suppressed. Problem solved!

The suppressed way will probably work but with lighter loads it can have issues and not always lock back.   Especially with a 12.5.

A lightened carrier probably won’t do much as far as helping cycle either.  For whatever reason the Acr doesn’t gain a bunch of reliability with undergassing and light bolts.  It might help some but not a whole bunch.

During my testing a light bolt passed testing at the exact same gas port as the standard weight.

The only exception is 300blk

I would Trust BigDog as he has probably the most time on the platform in non standard configurations...

I second this statement.  I felt confident in relaying info after multiple people's anecdotes.... But bigdog is the Gun Jesus of the ACR for sure. Sorry, guys

ADCO did mine years ago.

I did not remove the gas block.

It’s surprising to me to hear that it wouldn’t work unsuppressed. I swear I’ve talked to a few people that cut without changing anything and had no issues. It’s pretty commonplace on the AR’s.

Either way I’d cut a barrel and see how it goes.

I got my ACR shortly after they were first released.  ADCO cut and profiled the barrel.  I don't believe they opened that gas port.  This was when people were having problems with the guns being under gassed.  Rather than send the whole thing back, I put a vented set screw in the vent hole (on the front of the gas block).  It's run 100% since, and the 1/9 barrel has been plenty accurate.

When my form 1 comes back, I'm going to have class 3 machining cut the 1/9 barrel back to 12.5", and pick up a factory 10.5" barrel.

Salad days