The Kuehl upper should run well out of the box. I have a Kuehl upper that runs great, but I had to file down the feedlips on a couple of mags as they were sitting higher than my other mags and causing it to jam (ejecting on the feedlip). This problem was not related to the upper. It was due to the manufacturing of the mags. Before I used my Kuehl upper for the first time, I polished the rails and it functioned extremely well. I'm not sure if this polishing was necessary for reliable functioning, but I did it anyway. I did find that after shooting a brick or two through the kit, the recoil spring was not strong enough to strip the first couple of rounds on a thirty round mag. I ordered a $3.00 recoil spring from Lakeside and cut a few coils off the spring. The tension is stronger and I have no problems shooting with a full thirty round magazine.
Here's a pic of it:
[img]http://home.netcom.com/~brownhen/sitebuildercontent/sitebuilderpictures/.pond/m16-22wcinchedmags.jpg.w560h319.jpg[/img]