Yep, Cav Arms was the only one worth a damn, and they're out of business and in deep doo, doo with the feds.
Seems they had out of house sub-contractors actually doing too much of the plastic molding and actually "making" the receivers, rather than Cav Arms themselves. They were actually given a chance to change, but kept on doing it and got busted. Along with other violations and irregularities.
Well, the Bushmaster carbon lowers.. They may be ok, I haven't heard tons of bad about them, but I'm unsure if they're even available.
Cav's receivers (I used to own one) were a two-piece assembly, a left and a right half. They'd subcontract out manufacture of the halves to a plastics outfit here in PHX, then seam the two halves together in their facility.
ATF decided that the contractor having both molds at the same time (left and right) was essentially "constructive possession" since someone could just epoxy together two halves and make a gun. Or, just hold them together really tight and then slap an upper through the pin holes and the upper would hold it together, more or less.
So, they told Cav to only let the manufacturer only make one half at a time, or split manufacturing to multiple vendors (left only, right only).
I guess Cav didn't follow through on that.
However, I still love this picture from the "raid!11!zomg!eleventy!" on Cav when the ATF decided to finally shut them down:
To the OP: Meh on the Plum Crazy and similar style polymer lowers. Yeah, it's $90 or so for a complete lower with parts... but it's only another $75 or $100 to get a proper aluminum one with better parts. The LPK trigger/hammer/etc are plastic in these things, too. Yucktastic.
