Just got back from the range. I tryed out my new build. It has a CMT lower, a Model 1 upper
and colt ar 15 guts. Now, after fireing one 20 rd mag I took a short smoke. When I started back fireing I got a double about the fourth
round (said to myself WOW) and keep on shooting. Then about the 10th shoot it doubled
again. I found that if I held the trigger down after a shot and reset my sight then released the trigger the gun would fire again. It worked like this for about three more would be doubles. It seems that I was getting the double in this order: one shoot with the trigger pull and a 2nd shot with the trigger release. Anyone ever heard of a deal like this? Know how to fix it?
Want to buy a post ar15??? ( that part was a joke Mr. BATF ) OK, I need help so I don't have to live with Bubbu for ten years. Someone, anyone?

Do a dry fire test by holding the trigger back while you cock and release the bolt. Then slowly release the trigger. If the hammer lets go as you relase the trigger, your disconnector is not holding its' notch  at the back of the hammer w/enough engagement. If it's only doubling part of the time, chances are you can correct the problem by removing the disconnector and lightly filing the underside of it in front of that "hump" that has the pin hole in it. This will cause the hook on top to move slightly forward, and give you a more positive engagement.

Worst case scenario is that you'll need a new disconnector; a $3-$5 part [:D]. Don't panic; it's happened to a lot of us.

Worst case scenario is you can have a round go off out of battery. ( I think )

You don't wan't to shoot this rifle again until it's fixed.

 I could be wrong here, but if your weapon's doubling is due to malfunctioning components you have not "created" a machine gun.  Your weapon is purposely designed to fire only one shot per pull of the trigger but due to a malfunction of some sort it is firing more than one shot per pull.  As long as you fix this issue ASAP I doubt anyone will hold this problem against you as you have not willingly attempted in any fashion to create an NFA weapon.  That being said....I'd attempt to locate the source of the issue and fix it as soon as it is feasible...or sooner.

My friend and I had the same thing with his Buhmaster Bullpup, and we both enjoyed it yelling with excitment everytime it happened. We took it to a local gun smith and he warned that shooting it agin was not a good idea. After he explained what could happen, my buddy sent it off to BM to be fixed without firing another shot.

                                      KZ

My first thought would also be that disconnector needs to rotate slightly forward for better engagement.

Follow "shamayim's" instructions on filing the disconnector and you should be good to go!!

A good way to bench test the disconnector is to:

1. Pull off the upper

2. Cock the hammer

3. Now..., while closely watching the trigger,  pull the hammer farther back, if the trigger moves forward, even slightly, the disconnector needs to rotate forward.  If the trigger moves forward continue to step 4.

4. Slightly file the under side of the forward foot of the disconnector where it contacts the trigger plate.

5. Repeat steps 2 & 3  
  Repeat step 4 if needed.

RU4FREEDOM---out