I have wanted to build an inexpensive AR to use on the farm. I was also intrigued by the article "The Mujahadeen AR-15" where this fellow does a 80% lower with hand tools only.
I started with a cast lower, a flat top Rock River upper, and a J&T lower kit. Also had a lower blueprint in 1 to 1 scale.
I only used hand tools, no drill press, no 100 dollar jig, no mill. Everything went well fitting and drilling, only a small mislocation on the trigger pin hole, but a little JB Weld (swore I would never use the stuff...)
and I was good to go.
I function tested the lower, all seemed good, so I did a live fire with a borrowed upper. Wanted to make sure all was well before I put a finish on the lower.
It worked fine, 100 rounds with 3 different mags, no problems. Some Norrells molykote, and an hour in the oven, it was done.
Now to the upper. I wanted a 20" 1 in 12 for 55gr bullets. Got one, removed the FH and lug, moly coted the surgery areas, and the barrel was ready to be mounted.
I have read about using the upper vise sleeves vs the (it will never work, etc) barrel block method. I had a barrel block, a good vice and a lot of experience with delicate mechanical assemblies. I mounted that barrel up in the vise block with a silicone rubber liner to protect the barrel finish, and the barrel nut pulled down just fine to the receiver. No distortion, no damage, no agony. Worked just like the mil manual said it would. I was real leary of clamping that flimsy receiver in a vise no matter what kind of protection it had.
Now I had an AR that consisted of a Colt barrel, a RR upper, a Bushmaster bolt, A home made lower with god knows who made the internals, and a colt buffer and stock assy.
I was tempted to test fire it like you would a new black powder rifle (tied to a tire, fired with a string), but I went ahead and fired it from a normal standing position. I had checked headspace, so was only really concerned with functioning.
I started with my rattiest mag. One shot, check for lock, worked. 2 rounds, perfect. Different mag, 5 rounds, perfect. Different mag 10 rounds, no problems. No doubling, no FTF, no FTE.
Did a minor windage adjustment, and went through another 120 rounds. This thing works. And it throws all the brass in a neat little pile so I can pick it up when done! All shooting was standing, offhand, at 50 and 100 yds, so no real serious accuracy work done. I got the sights zeroed ok, and the groups were about normal for me with a rifle.
My only other 223 experience was with a mini-14 (spit) 15 years ago. I was amazed this AR shoots a nice group. I was used to the mini shooting a pattern that always strung up and to the right as I shot.
This lower may not last forever, but everything fits and functions. I am working on a RR lower also, but am having a terrible time getting fire control parts to work. I think I have run into a tolerence stacking problem with the RR.
My rifle cost about 450, and it should earn its keep on the farm.
Edit to add: It weighs 6 pounds 14 oz. without the rear sight. Not bad for a 20 inch barrel.