Ive never had problems slamming the mags into the magwell. Sometimes I slam them, sometimes, just for show, I slide the mag in enough to stay, then just tip the gun, and jerk it into the magazine... the crowd at the rec ball field usually loves that.
What Im saying is, I wouldnt worry about paint breaking in the mag, unless you hit the little bar and spring holding the paint in before its seated. Then you may lose a round or two into the magwell, and crush them as you seat the magazine. Then, good sir, you are hosed.
Captain of the Camo Bandits Scenario Paintball Team.
"Who Dares, Wins."