I have an older JA Ciener kit that I use in an upper that I put together for it, though I'm sure for plinking that it would work fine in any of them.
I am using an older 1/12 twist 20" Colt barrel that I'm sure has a few ten-thousands of rounds down the pipe. I found it used on ARFCOM, so it's hard to say. I have it hooked up to an A2 upper, no optics used...just the iron sights. It is plenty accurate enough for my uses
It functions about 99% so far with Federal bulk pack ammo, no complaints at all.