I have an OLY SGW lower that I put a JT M4 upper on and they did not fit together correctly. The takedown pin holes lined up, and the pins went through, but the upper protruded into the front of the mag well by about 1/8th of an inch and will not allow a mag to be seated.

I have had this upper on both an Essential arms, and another Oly lower without any problems, but have never used this lower with another upper, and do not have one availible to try. Has anyone else had this problem?

This did teach me a valuable lesson though, make sure everything works after fully assembling the weapon. I made sure that a mag could be seated after I had put the lower parts in, and did a standard mechanical function check with the upper on, but never tried to seat a mag in the fully assembled rifle until I took it out to fire it. What is even worse is that I was going to sell the rifle, but when it didn't sell by the weekend I decided to shoot it. Boy am I glad that it didn't sell, last thing I want is to give someone a bum deal!

I have read there is a potential legal problem with building a rifle and then selling it, that this can be considered manufacturing the weapon.  [i]I am not a lawyer and certainly not an expert on this,[/i] but it is something you need to look at before selling a rifle you have built.

Wingman26:
I think what is the issue here is if you are building firearms for sale without the proper ffl. This would be ok in this case but lets say you built 10 guns just to sell this year then I think the ATF would look at it as dealing without a license.

I never intended to sell this rifle, I have had all the major components for 5 years, but becuase of where I have been stationed, it has been unpractical to finish putting it together. Decided to sell it instead of keeping it around so that I could finance a pistol.

I would just like to know if I have a faulty lower, or if some uppers are just uncompatible with some lowers. If some are just uncompatible then I will sell it in pieces.

I had the same type of problem with my oly lower.  It wouldn't allow a magazine to lock in when the lower and upper were attached, I sent it back and was told that it was a special type of lower that was made to only fit certain oly uppers and my choices were, grind the upper to fit the lower or for $150.00 they would make another lower with the same serial that would fit.  E-mail me if you need more info.

I think that the stripped lower is the only thing considered a firearm by the BATF.  Everything else is just accessories added to the lower.  So, unless you're manufacturing stripped lowers you're not really manufacturing a firearm.

I'm sure someone will correct me if I'm wrong [;)].

Hoppy

Sounds like this might be your biggest problem!