I have a upper made by Spikes. Uses Blackdog magazines. Works great. I believe they quit building those because of patent infringement. The exact same design is built by Tactical Solutions.
There are a LOT of companies that make .22 uppers. The CMMG "pattern" was/is the primary pattern and their original magazines were the bomb. I do not think there is a patent infringement issue. CMMG patented their adapter, there are several "patent pending" and actual patents for little pieces and parts, but none for a whole AR22 upper with a blowback bolt and collar with a dedicated .22LR barrel.
The issues come in terms of reliability and accuracy trade-offs. Most people run .22LRs into the ground with no cleaning. When those same folks insist on 1 MOA AR22s, therein is part of the problem. You can get a Bentz (or other match profile) chamber and get great accuracy, but then don't expect it to run 500 rounds of Golden bullet. Carbon rings, lead rings, are a thing with .22LR, especially with tight chambers. AR22s with feed angles, elevation of the magazine w.r.t. the chamber, feed tension, bolt speed, bullet profile all create a very finicky platform. I made what I consideedr to be the best all-around AR22 upper on the market for several years. Patrick Kelley has one (as do several other top shooters), he loves it, one of his "Favorite Sticks" and the one he uses to "play" the Christmas Carols with. I have 2 of them, one with 100K rounds through it...still shoots 1 MOA at 100 yards with quality ammo, but not match grade ammo. I spent over a year on R&D. Light, fast, reliable and accurate. I tuned every single one personally and ran them for over 100 rounds afterwards and they had to be 100% or they did not go out. BUT, and I say this with all due respect, they were more headache than they were worth. 1 in 5 ended up with, well, a guy (or gal) that wanted to run 5K of Win Wildcat or Golden Sabre, without cleaning, used a trigger or lower that was out of spec, or used cheap magazines. In some cases, more than one of these reasons why "we can't have nice stuff." I got a few sent back for a retune with dremeled chambers and collars, some with so much crap in the chamber I am shocked they ever got a round to ignite. I no longer make them for those reasons.
If you want to duplicate those, I used Velocity bolts (with the collars) with NiB coating and what they make had some enhancements based on what I did with their bolts. I used Beyer barrels, and he still offers the profile I spec'd which is a 16.5" UL barrel. I used a Nordic upper received. I finished them off with the Carbon Arms Carbon Feather HG (barrel nut torqued to 75 ft-lbs), PlugAR in the FA port and a DPMS dust cover. They will run with most match triggers with a reduced mass hammer.,.but I did not, and do not recommend Mil-Spec or Hiperfire triggers for them. Empty buffer tube. Tune the mag/mag catch so that the bullet is pointed directly into the chamber right before the rim releases from the feedlips. For plinking or high volume shooting, use Black Dog mags with CCI coated bullets, or Winchester M22 bullets tumbled (or shaken) in media for 5 minutes to remove the lube. For match grade (1/2 MOA), I used Eley, but several others work as well. Put a tiny drop of CLP on the first bullet of the magazine.
I am currently sponsored by both Nordic and Tactical Solutions, and both have very good quality AR22s. The accuracy is not quite as good as what I sold, be decent enough with match ammo. The SBX barrel from Tactical Solutions is a great choice for suppressed.
https://www.tacticalsol.com/ar-22-series-uppers/ar-22-sb-x
