This mag extension is a vibe. - TRYBE Defense Glock 17 +4/5 Rounds Magazine Extension Base Pad

This bad Jackson buffs my 17rd mag to 21. Now for my battle pistol that's a healthy amount of pewpews. Oh yeah the spring provided with it was just simply not strong enough to reliably cause last round hold open. My 21rd Pmag donated it to this setup and now it holds open like a boss. Makes sense considering that's how many rounds it holds so it all worked out.