So I just finished my first lower build, and I noticed that any mag I put in it ("any" meaning GI, PMags, and Thermold) all wobble a bit. Now, this is just the lower. I don't have an upper to attach it to so I can't tell if this is normal for a lower or not when it isn't mated to an upper.

The lower is a MEGA/Red River Tactical.

ETA: Should I tighten up my mag release? Because it wobbles a little side to side too.

normal

"Wobble a bit" can mean different things, first don't do anything until you test them with the upper and lower put together, the mags fit into void in the upper pretty closely, which will likely cut down the wobble you experience.  A little wobble is normal and its usually a little more when its just the lower and no upper.

Play around with the mag catch tension when the mags aren't catching/releasing like they should.   It might effect the wobble, but if the rounds feed reliably during firing, then there is nothing to worry about.