Since ACR uses standard AR15 FCGs, solutions should be the same.
Was shooting my ACR at the range and had several trigger reset problems. Occasionally I dont feel the click of the reset when I let go of the trigger. So obviously when you pull the trigger hammer doesnt drop. However if I push the trigger forward I can feel the trigger click and reset. Sounds like a weak return spring tension or something is dragging?
Check the disconnector spring.
Look for a burr on the hammer or disconnector.
break in? how many rounds have you fired through the ACR?
only shot about 200-250 rounds of various stuff so far
Here we go with break in periods…how is it that a $3000 piston rifle needs a break in period? An issue like this is QA, it should have been squared away before it left the factory.
checked out the notch in the hammer where the front of the trigger engages it, I didnt see any burrs. Didnt see any burrs on disconnector also
The owners manual of many performance vehicles recommend a few hundred miles of easy driving before you put the hammer down. Is something similar not applicable to firearms?
ive had a similar issue with one of my ARs a while back. It was strange because one range session it was acting up. Then the next time I took it out it didnt act up in the 150 rounds I shot and hasnt returned ever since. No idea what happened, maybe something got worn in. I’ll have to go back this weekend to see if anything changed. I took apart the ACR trigger pack and put it back together (not as easy as an AR) thats about it.
The disconnector felt like it had a tad bit of friction as compared to one of my ARs that has no issues.
The comparative complexity and costs of the machines would make break-in with one more reasonable than the other.
If we follow the car analogy though, the failure reported here would seem be something akin to the car running only intermittently when you step on the gas. 
Unless your rifle has an engine, I don’t see how you can make a straight comparison like that, especially with a rifle’s trigger group.
A brand new rifle failing to reset is not a break-in issue, something internally was not manufactured or installed correctly. For example, a burr may wear down over time, and your rifle will start resetting properly, but that doesn’t change the fact that the part wasn’t made correctly in the first place.
Contact Bushmaster and or keep shooting the shit out of it. Don’t depend on it to save your life in the event you need a rifle until the kinks are worked out. That’s the price one pays to be the first kid on the the block.
No, it’s not.
Let’s be fair guys, it’s expected for the ACR to have some issues considering how fast it was rushed to market. Oh wait nevermind…it took almost 5 years. IMO at this point there’s no excuse for any failures on those rifles. What a huge disappointment…
I dont see it as an ACR design issue when it uses normal AR FCG parts. Not like its proprietary parts. Ill try it out again this Friday.
You may have a primer part or some kind of debris floating around in there.
when I took it apart I didnt see any debris or burrs. Im starting to think its a weak trigger spring as mentioned by nickdrak in another thread:
Doesnt the ACR use a standard AR Milspec trigger group housed in a contained “drop-in” unit?
What you describe is typically caused by a weak or overly modified (bent legs) trigger spring.
I’ll probably give bushy a ring later this week.
'Let’s be fair guys, it’s expected for the ACR to have some issues considering how fast it was rushed to market. Oh wait nevermind…it took almost 5 years."
Let’s be accurate, the prototype Masada was introduced at SHOT 07, extremely early in its development. Shortly after SHOT 10, guys had them in their hands, and in that time frame, there was a whole shift in design “ownership”, and a semi shift as Rem got more involved. Now if you were talking about the SCAR or some other rifle, then 5 years may be the case.