Today it is possible because of military spec’s to buy an upper from one manufacturer and purchase a lower from someone else. Both need to go through an FFL dealer to purchase. My new AR is a hybrid where the Colt upper is mated to a mil spec lower. See Image below.
I shot 40 rounds (no glitches) with my son who also already owns an AR like semi-auto. Accuracy at 25 yards with open sights is a half inch. I had a Tasco Red Dot sight already so we mounted it too and sighted it in. Groups were similar with a red or green dot Image.
Back at home we cleaned it, took out the bolt and firing pin for cleaning and inspection. It was an easy task that looked harder than it was. Taking the forward and rear pins out then separate the upper from the lower. Of course many of you know this already. Next is to get a sling that works for me and connection points that I prefer. Forward is a hand grip that makes better sense than holding the picatiny rail. Recoil? What’s that? Of course it had recoil but it was not noticeable at all.
I will run this rifle through its paces for accuracy so there is lots more to come.