Thingiverse
AR-15 Vice Block by ya3dpc
by Thingiverse
Last crawled date: 4 years ago
Based on my previous thing, this allows you to mount your AR-15 into a vice to let you work on it.
With a high enough infill and proper print orientation PLA should be strong enough for your needs, but if you're going to be cranking super hard on your rifle, e.g. replacing a barrel, you may want to opt for a stronger material like nylon.
UPDATE: Initial design had the magazine catch notch too narrow. Updated and now completed lowers will lock onto the vice.
With a high enough infill and proper print orientation PLA should be strong enough for your needs, but if you're going to be cranking super hard on your rifle, e.g. replacing a barrel, you may want to opt for a stronger material like nylon.
UPDATE: Initial design had the magazine catch notch too narrow. Updated and now completed lowers will lock onto the vice.