Fixing Failure to Feed Caused By Magazines
Most mags have some back and fourth movement. If you are getting failure to feed jams from the bullet nose hitting the top of the chamber opening, put some aluminum duct tape on the front of the mag to keep the upward angle down.
Hitting the lower part of the chamber opening, put tape on the rear of the mag.
If this solves your problem, use some thin plastic put on with super glue.
Often this will solve the problem.
Experiment with the thickness until you get reliable feeding.
Check the lips on the magazine. The plastic lips will wear over time. If this is the case, it's time to buy a new mag.
Buy mags with metal feed lips when possible.
Best regards, John K