Im wondering if your buffer spring is weak? Try replacing your buffer spring with a nice milspec weight chrome silicone one. A tone of brands sell them, Larue, Sprinco, Tubbs, Wolff. Sounds like your buffer spring might be weak and the new mags are outpacing your bolt carrier return rate. You can stretch your existing spring to check prior to purchasing but for around $20.00 for a chrome silicon spring you cant go wrong to gain a good deal of lifespan. I think I have old Wolffs CroSil in mine, never had issues with them. Doing rebuilds and thinking about new springs. I wouldn't go any higher than your OEM spring weight because it can cause excessive bolt wear, case lip damage, and pressure issues. A heavy spring allows the pressure to increase and slightly better muzzle velocity, but the cycle rate is slowed back, which can reduce felt recoil, then the return cycle is faster and can cause issues.