Here's my story...
Was up in northern MN today shooting with a gun buddy. Brought out the new 9mm AR and ran a mag through it, sighting it in with the Vetcor reddot at 25 yards. Got it close enough (and this barrel shot pretty nice and tight groups too....only 25 yards, but is it just a 9mm). Decided to run another mag, still perfect, no issues. Decided I needed to bump a 20rd mag through it, because 9mm ARs typically bumo to beat hell. It was a double, then the rest of the mag in one string...ran perfect.
Long story short, a couple more non-bumping mags later I decide to bump again.........bang, bang, bang, bang....BANG-POOF. The half loaded may is blown out the bottom of the gun, cloud of smoke, strang sounding bang. I knew right away what happened. It isn't that uncommon for a blow back gun to have an OOB when bumping.
I wrote it off as no big deal, but then loked inside the bottom of the mag well......there were pieces blown of the mag block here and there, and the rest of the block that was still in the magwell was in a number of pieces. I ended up pulling it out of the lower in the already broken parts....and then took these pictures of what I had left in the pile:
Doesn't appear to be any other damage to the gun anywhere, nobody got hurt.
So, this block was great, but if you want to bumpfire you risk getting an OOB and it may destroy the mag block.
I am not sure which direction to go this time........probably get a CMMG designated 9mm lower.
I would still reccomend this block, as long as you have no intentions of bumping.