A few years back there was a company called Ramline that made a 30rd mag for either the AR15 and Mini14. From what I understand, it only worked so-so in the AR15, it didn't activate the bolt hold open on last round on the AR15, but feed okay. On the Mini14 it function okay. The Ramline company is now gone, but I bet there are some floating around the internet for sale. I would purchase one and find out how they work in your respective gun and with some type of return gurantee if it doesn't function to your satisfaction.