I used the CMMG conversion bolt until recently and it works fine. Fed great with any decent ammo and plenty accurate for plinking. A few weeks ago I bought a CMMG complete upper with stainless bolt and it works great too. I got it cause I didn't want to shoot the rimfires through the 5.56 barrel, and I thought the .22 upper would be much more accurate having the proper twist, diameter and chamber for the rimfire round. You can buy a complete .22 rifle for what I paid for just the upper, but it might have a polymer upper and lower reciever, the CMMG is all metal, so feels like a "real" AR.