I’ve always thought that Centurion Arms C4 rails with FSP cutout made a lot of sense. They’re a clamshell design that lets you remove the rail without removing the FSP and attaches to the M4 barrel but. The C4 comes in Mlok and would snap right on a Colt upper. As already mentioned, 14.5” mid-length can be ammo sensitive. The current climate is a reminder to have something that’ll eat steel case and whatever’s available.