I found a nice bushmaster piston based upper. Just finished building my second one with an upper I got from my friend. It is a spikes tactical lower with Vltor MUR-1A upper and a bushmaster bull barrel with a Youngs national match BCG and a RRA 2 stage trigger. Super happy with both of them but I would like to get a few more things for them. like miad grips and maybe freefloat tubes for them.
Forgot to mention they are both .223.