I' ve never had a problem shooting +P' s out of a Glock, or +P+' s for that matter. Where the " problems" come in is when you shoot lead bullets or get a double charge. Also bullet setback is a problem. If you want to shoot lead through a Glock you need to get an aftermarket barrel. KKM makes one. They even make a 6" barrel for your 21 called the " Hunting Barrel" . Check here for further details....

http://www.glockmeister.com

http://www.glocktalk.com