WD91, I went down that road too, also with pretty good success.
Picked up a side charging upper in 300BO. In an effort to make it as quiet as possible, disabled the gas block. Making basically a bolt action AR.
Shot it sub-sonic and suppressed of course. All told, made it all real quiet. And shot reasonably well.
Shot it using this bullet, mold from Accurate Molds, 210gr bore-rider.. Lubed with 50/50 Beeswax and vasoline...
Also shot it as designed, semi-auto, shot just fine, no feed problems....
Ended up sending it down the road, have a BO in a Contender....