AR platform magazines are available in different round counts but should not be filled to maximum capacity.  When shoved full to complete capacity we run into issues inserting a mag when the weapons bolt is in the forward position as it will be on a proactive reload.  Pushing harder to insert the magazine and forcing it in is not the solution.  In general, it is safe to go with a 28 round count in all 30 round mags.  Some manufactures have already made room for this problem by leaving room for an additional 2 rounds while others now sale new products labeled 32 round magazines.  No matter the brand or the number of bullets it advertises to fit do not fill these to max capacity.  I learned this lesson years ago during a proactive reload in the carbine portion of a 4p tactical team competition where the range officer watched my struggle of trying to get a max capacity mag into the AR.  After realizing I was killing precious time on the clock I dropped the mag and went for another off my plate carrier.  Lucky for me the next mag went smooth into the mag well with a nice securing click and good tension when I pulled back for verification.  That magazine had been loaded by a SWAT operator that was on my team, he loaded it with 28 rounds.  I was now able to get back to work and finish the course.  Don’t learn this lesson too late… fill those to mags to 28.