For around 250 bucks you can get a 6 arc upper from bca. If it doesnt shoot pull the barrel and replace it with another and your still money ahead. They longest they offer in 22 arc is 20". I would want at least 22" in the smaller bore. The larger 6mm will be more efficient in a sub 24" barrel depending on intented use. I believe they offer them in 24" though. Ive used a bunch of their stuff and I doubt some of the over priced stuff from some of other companies is any better. I've got rifles thst will shoot little bitty groups assemble on their uppers. Ar accuracy is all about the barrel. They are also 8 twist if you want to shoot lighter bullet.