Anyone have experience running one of these for a long time?  I got one along with a 9mm upper in the EE and someone modified the feed ramp pretty heavily, but it functions 100%.  I am debating getting a dedicated lower, but with a functioning magwell adapter I'm not sure if it's worth the extra $$.

I used one for probably about 3000 rounds and multiple range trips before I picked up a CMMG 9mm lower.

It worked just fine with C products mags, and a lot of mag changes but I wouldn't call what I did with it heavy use. I feel like I could break it if I landed on it with a magazine in it at the right angle but that may be unfounded.

If it's just a range toy I'd use it till it broke then go from there.

i use mine all the time a couple thousands rounds down range.

even managed to crack it in a few places when I had an OOB explosion. Still runs like it did with out any issues.

Personally I will some day go ahead and get an actual 9mm lower but I will have to stamp it and wait a long time to use it.

I love how easy it is to change the caliber on my registered SBR lower. Pop the pin out on the bolt catch remove the block and back to .223 and .300 I go.

I had to make modifications to my promag block but it works fine so far.

What kind of mods have did you have to do. I just put one in also the first 5 rounds were fine then stove pipe. The last shot open seems to work.

I had to polish the ejector on mine, it was rubbing on the bolt.  I found anything that slow bolt speed made my promag gun less than 100%.  I had 700rounds on mine and then went to dedicated lower.