FM Products does not support the following items, using these may void the lifetime warranty associated with our uppers;
1) Aluminum Cased ammo. Blow backs have a much higher pressure spike in the chamber than a handgun. Using Aluminum cased ammo in a blow back PCC is dangerous and will void the lifetime warranty of an FM Products Upper Receiver.
2) FM Products does not support import magazines besides OEM Glock magazines. We recommend Magpul, OEM Glock and ETS magazines only.
3) FM Products does not support Spikes Glock style lower receivers. The LRBHO has changed several times, and requires consumers to modify the FM Products upper, to make egress for the Spikes LRBHO.
The FM Products upper is cut to the Colt spec, and therefore, we have no plans to deviate from that. Modifying your FM Products Upper to accommodate a Spikes Tactical Glock style lower will void the lifetime warranty on our PCC Uppers.