I have 2 BCA uppers on printed lowers. They work fine. They are heavy. LRBHO (last round bolt hold open) needs a special 22lr replacement if you use a standard AR lower design. deAR22, HD22, EZ22 lowers should all work if memory serves me.

DeAR22 and use the stock upper, or do like I did and print a BCA upper (already notched for 22LR side charger) and drop it on your favorite lower. Files are sailing on both of those - you will want the rail version since the 22lr bolt doesn’t really need a buffer tube (unless you just want to have a buffer tube mounted brace/stock). Oh, and I also ended up making a modified proto-barrel using carbon tube and .375mm .22LR sleeve from Chaszel. I can send you the STL’s if you want - even made a jig to get the extractor filed down easily :)

I will warn you up front - that 22LR from BCA is heavy for a 22. If I had to do it again I’d just use their bolt or make one (working on that jig now too hehe) and print/build anything else.

Another fun build is anything 10/22 related. You can even print a 10/20 bolt and add some additional weight to her so she can cycle std CCI (1050fps) rounds all day long. Plus the 10/22 just fuckin’ rocks for plinking.