I guess, just for clarity sake: I know what a dedicated .22 LR upper is, my question was effectively "What do you mean your CMMG conversion worked better when you got a .22 LR dedicated barrel?" Because a dedicated .22 LR barrel wouldn't need a CMMG conversation device.
For your convenience, this is my original post:
“Short” story: My CMMG 22LR AR-15 Conversion Kit ran great in my AR carbine with near perfect reliability. However, once I put it in my new, built by me, dedicated 22LR AR, it was not nearly as reliable, with zero to 4 malfunctions per 25 round mag, regardless of ammo type and brand.
Knowing that the conversion kit is blowback operated that does not function with the AR platform buffer and recoil spring system, that this firearm would be a dedicated 22LR, and that I want this gun to be lightweight, I left the receiver extension/buffer tube hollow. I did NOT install a buffer and buffer spring.
Long story short: I have now put a standard AR-15 weight buffer (3.0 oz.) and recoil spring, and the gun works perfectly (damn near it anyway). Before I put the buffer in, it malfunctioned around 12% of the time. With the buffer and spring, I shot 600 rounds this weekend and had only one malfunction (a single cartridge nosedive). CMMG should have this information front and center like RightToBear-dot-com does on their site (see below), or at the very least very available in a Troubleshooting section. As a matter of fact I plan to write about this to them. They’ve been very responsive in the past when I have contacted them (for other reasons).
For those who are curious, I am of course using the same ammo now that was malfunctioning before I put the buffer in. Those two ammos are CCI Mini-mag 40 grain Copper Plated Round Nose, as well as Aguila Super Extra copper plated 40 grain RN.
I discovered this fix by accident. I had tried many other things before this, by the way. I was on the Right To Bear vendor’s website. I read what you can see below in the screenshot. Ultimately the buffer and spring help to stabilize the 22LR bolt carrier. Looking at the bolt carrier and the way that it inserts into the receiver, it looks like it will not move during operation. However, when it cycles back, it moves the carrier ever so slightly such that it can cause malfunctions/jamming.
If there were a rimfire forum here or an AR forum, I would have posted there. There is not either of those so I posted in this general topic forum.
I hope this helps someone!