Lower receivers aren't semi-automatic. Only the upper is. There are bolt action uppers you can mount on a lower. Buy Glock factory magazines. They have the steel liner and are more durable. I have a Glock 19 and two Ruger PC9s. I use a G19 15 rd mag when I carry my G19 and a 17 rd mag in my mag carrier. I have a dozen 15 rd and a dozen 17 rd magazines and four 33 rd mags. I can use any of them in my Ruger carbines. I have dozens of AK and AR mags. My advice - buy magazines even of you can only afford a few. Keep the receipt so you can prove you owned high-capacity mags before the ban. Doesn't matter if the receipt is just for a couple mags and you own dozens - you still have proof of pre-ban ownership. Good luck!