After owning a few 9mm chambered AR15’s, I found I don’t trust the drop-in magazine blocks, in regard to over-all reliability. However, I don’t have much experience with the factory pinned-in Colt offerings. Though I have a little trigger time with a transferable select-fire specimen, it isn’t enough time to consider it educational.
Below is a personal build I did on an almost all Rock River Arms metal parts. I had a small problem getting the iron sights to work for close range.
More to the point, I had feeding issues with Colt brand magazines as well as polymer Bushmaster brand, C-Products (shown above) and both Rock River Arms and custom Vector Arms modified Uzi mags. An improved feed ramp was desperately needed. Rock River obviously figured out they needed a better solution and announced a dedicated lower was coming…just after I’d finished my build. More than a year later, I actually saw one in a gunsmith’s workshop; by then I’d lost interest in using RRA parts. I sold the firearm once I gave up on the RRA magazine adapter block.
I do like other carbines that use sub-calibers, but what I was after was AR15 ergonomics, with a Magpul BAD lever, in a 9x19mm.
Enter the Custom Double Diamond 9mm SBR AR15 type build with a Spike’s quad-rail. There is actually a barrel in there but it is designed to allow the suppressor to be protected back inside the handguard.
There was one major problem with this setup. The bolt catch activator (the actual riser that gets lifted by the magazine tab, which lifts the standard bolt catch) works sporadically once the weapon is dirty. Add a suppressor, and being direct blowback, dirty becomes its natural state. The actual bolt catch needed to be removed (with a punch tool) to clean out the build-up.