Building this AR in 9mm and I only need the barrel and BCG to finish my build. Are there any differences between the PSA glock BCG's and other companies? The reason I ask is because PSA is out and I was looking at other companies. Also, there are several companies providing barrels are they all compatible?? I've built dozens of 556 and 300 blackout but I'm get stumped on this 9. Any help would be appreciated. Thanks!!