current pap without the rail is a gen1 N-PAP. They have a bolt made only for a single stacked mag. I would stay away from that. The one with the rail is a gen2 N-PAP. It has a bolt that will work with all common double stack mags. There is also more butt stock options out there for the gen2 due to it having a squared off receiver. The gen1 has a slanted receiver. I own a gen2. Its a great gun. But again I would stay away from the gen1.