As part of messing around with a Glock 19 in USPSA Open, I got some longer mags that meet the 170mm requirement for Open.
First, I should say that longer magazines can be sensitive to overall cartridge length, and PMC and Lawman is too long for some mags. Syntech 150 and 124 is shorter in overall length and seems to work in the longer magazines. 28 rounds seem to work in the 170 length.
Starting from the left, is an ETS 170mm. These were dirt cheap and I was pretty skeptical. Looking through the translucent mag body, at the cartridges and spring with a fully loaded payload, is not for the faint of heart. As in, that is supposed to work! Surprisingly, so far they have been reliable.
Next is the Magpul 170, but I don’t have enough rounds through them to express an opinion. I like how the cartridges feel loading the ETS more than the PMag.
The Taran 140 extension is my go to solution for a Glock in CO and is as close to bullet proof as any extension is in my experience.
Next is a Taylor Freelance 170 extension that goes on an OEM magazine. Definitely sensitive to cartridge overall length as at about 24 Lawman cartridges, I got a wicked jam that necessitated removing the baseplate and a lot of cursing to resolve. Work fine with Syntech.
Finally, the high dollar solution is the MBX 140 and 170mm magazine options. They have worked fine so far. The mags rattle a bit unloaded, but feel right when loaded. The advantage of the 140 is you can get 23 or 24 rounds in, at the cost of no locking back when open.