I have an old Rick Kuehl .22 upper that uses a modified Ciener bolt with the feed ramp on the collar like the Cmmg bolt. Does anyone know if the Cmmg bolt is compatible with the Kuehl upper with no or maybe minor modification?

The only difference maybe the diameter of the barrel and collar inside diameter.  As an example CMMG uses a .460 inside diameter collar whereas TACCOM, Model 1 sales and Spikes used a .500 collar.  I'd also measure the rails which hold the collar.  The rails are notched to accept the collar.  To change collars you carefully pull the rails to rotate the grooves out of alignment and slip the collar out.  I don't have a Kuehl upper to measure but I have a CMMG and Ciener bolts/rails and I have used a CMMG collar with my Ciener bolt.  I don't know if Ciener ever changed demensions on their rails or chamber inserts but if you get the correct diameter collar for your barrel I think your CMMG will work.

thanks for the reply. The ID on the Ceiner collar is .500 so I guess the question is will the Ciener collar work on the Cmmg bolt?

I put an Viton O ring on my smaller barrel stub.
It works OK with the larger collar.

Fork distance is similar.  Even if it's not a perfect fit, it can be made to work.

Just a follow up. I got a CMMG bolt and the .500 Ciener collar fit just fine. I just did a test fire of 25 rounds in my backyard and function was 100%. Of course I am going to have to shoot it a lot more!

Thanks for the update, glad it worked.