I had an issue with my ACR, and contacted Bushmaster about getting it fixed shortly after Remington bought Bushmaster. The RMA had it shipped there. Supposed to take 10 days.
Long story short, they couldn't (or didn't know how) to fix it, and basically sat on the rifle and paperwork. (Even with the paperwork and RMA information I was told to send with the gun) After a month with no word, it took me threatening to initiate a BATFE audit for them to actually bother looking for my rifle and contacting Remington to figure out what to do with it. At which point it disappeared again, (~2 months) and it took me bugging the fuck out of a Remington VP for my rifle to be tracked down at the Maryland facility. It then took ANOTHER month or so for them to come up with a replacement barrel, cause they couldn't just use a 1 in 7 twist unit that was sitting on the shelf.
At no point were they communicative about my rifle, and any progress on the repair was due to me badgering the hell out of them. I wasn't impressed. (They also performed the firing pin recall at the same time, and instead of the 2 30 rd PMags I was supposed to get, I received the ban state 10 rd mags. Which when inserted required the rifle to be broken down to remove because they were too short to grasp to pull out, and too tight to drop free under gravity.)
All in all, this lead to me reevaluating the ACR, and I decided that while it was a cool rifle, the lack of support or interest in supporting the firearm from Remington in case I had another issue was a serious liability. I sold the gun after I got it back and verified function.
I'm sure if its something like a 700 or 870, you'll have better luck than I did. Probably.