do they run?? with ammo prices the way they are now you'd have to be insane not to concider this option, but i want something that'll be reliable, as im concidering trading a very reliable ak74 for a sw 5.45 upper.

yes they run, but you'll need an M16 Carrier as the S&W has an ar15 carrier and you'll also need to use their heavy hammer spring (most likely). If you've got a M16 this is by far the cheapest way to feed it...

Don't forget this stuff is corrosive so make sure you clean it up when your done, there is plenty of threads describing how.

ok ive got an upper now, gonna sell off the ar bolt carrier, which buffer to get though, i currently only own an h buffer and a std carbine one, is 9mm overkill?

I run a 9mm buffer in my RDIAS lower with all my uppers , everything runs fine

would it work let's say on other "weaker" calibers ? like .222 ? would go lighter buffer to run full ?
I'm just being curious here.

ok finally got out to test fire the 545 upper, overall i am very pleased,  shot 300 rounds of bulgy surplus, 0 feeding problems but out of the 10 mags i fired (out of 2 cproducts mags that functioned flawlessly) I had one failure to fire, which looked to me like bolt bounce with a light tap on the primer, I am running a 9mm buffer already, as it breaks in will this become more of a problem? the rof seemed to be somewhere in the 650-700 rpm range as i could easily do controled 2 and 3 round bursts on auto. i really liked the way it shot though, i just want to make sure its as reliable as possible, I'm running a wolf extra power spring also.