Re: 5.45 x 39mm AR upper
Hey, as an option, Spikes offers the barrel and coated bolt carrier group separately. I bought those parts and paired 'em up with a nice receiver of my choice. I put a Troy rail on it and it came out nice. Get a stainless mid-length gas tube and low-profile gas block, and you'll be set. Do research on mags-that's the hard part to source. Well, not hard to find, but it's hard to find the one's that work. Opinions differ on who makes the best mags, but you have to get mags that are 5.45 specific. Due to the tapered case, the case shoulder dives down and the rounds hang up in the mag. I tried modifying a non-windowed 5.56 Pmag, based on something I read on another forum-don't waste your time. The 5.45 mags' follower is raised up in front support the tapered case shoulder and keep it from diving while feeding.
I have yet to shoot mine, I had to run off OCONUS to go work, but when I get back, I'll order a few different makes of magazines and see which ones are worth a darn. Be careful shooting ballistic steel at danger close ranges. (Yeah, I know you shouldn't shoot steel closer than 100yds, but it happens) I hear from a few people that the Russian surplus stuff is kinda bad about having the penetrator separate from the jacket and come back at pretty high velocity. Nobody died, don't worry, but you might get some nasty flesh wounds to distract you from training, or ruin your day. Wear good eye-pro.
I hope your project comes out good. Let me know how it goes, I could use your feedback in my project.