I've had a Kuehl M4 type upper for a few years now. Not too long ago, I purchased 3-9X32 Scope to see how well it would shoot. I had always thought it was pretty accurate, but when I shot it trying to get some serious groups I was disappointed (similar results as described by rocketman223). For me, it is no better than using my Ciener adapter with a 5.56mm barrel (1 in 12 twist).
I think the reason for the lack of impressive and consistent groups may be due to the seemingly larger chamber. Even when it was new, I could not shoot Remington brand .22s as the "blow-by" was a regular problem (every few rounds). In the beginning I did not think this was as issue as I like to shoot the CCI brand. But, 6 thousand rounds later (give or take), I get "blow-by" occasionally with CCI brand ammo. I never experience this problem with my Ciener chamber adapter. The chamber diameter is noticeably smaller on the Ciener adapter when compared to the Kuehl upper.
The Kuehl upper is a quality piece and I've enjoyed shooting it. Except for the "blow-by" issue, it is a very reliable package. In addition, Rick is great to deal with.
Dan