I feel like I should clarify my original post. If you already have an AR-15 and a set of tools then for sure I would recommend building a dedicated 22lr upper. If you don't have the tools then perhaps buying a M&P might make more sense (I'd recommend a Sig 522 first though). That said, any of the "conversion kits" can easily be adapted down the road to a dedicated upper with a simple collar. I highly recommend Tapcom when it comes to 22lr AR parts/barrels. Barrel - Steel 16"