BEST BANG FOR THE BUCK!!... Buy the ETS mags. They vary in capacity. 17 to 40 rounds.. I shoot in competition weekly. I use mostly the 40 rounders, whether or not I need all the capacity... .Usually no mag change required during a course of fire. AND the good thing is they are about $12.00 to $15.00 each AND they are warrantied AND WORK!!!..... Search the "net", BoTech and others stock them.... Now, if 40 rounds isn't enough?, MBX, and Taylor-Freelance, others have extensions w/ springs to get you over 50 rounds..... Be a little cautious in your ammo choice!, Glock mags seem to like a shorter over all length, to long and they will "nose" over and jam. I reload so I can tailor the bullet to what works for me. Mike