From the comments section:
Sold one to a customer, and it wouldn’t run with 5.56 ammunition. He sent it back to Bushmaster, and they sent it back, claiming that it shouldn’t be used with anything except .223 Rem pressure ammo, even though it had 5.56 stamped on the barrel. he sold it and bout a Century 20 in repro AR, and he said it ran better than his ACR ever did. "
I picked up 2 of them when they were the hot ticket…
Designed for someone 5’-2" tall… I had issues… front end heavy, big time… and sort of strange ergonomics.
I sold them both.
Was very tired of ramming my hand into the optics mount with the charge handle.