I test fired my modified 20SF yesterday with a new +5 mag extension. Loaded the mag with 20 Hornady 180gr XTP's, and got fail to feed malfunctions in the first 3 rounds. I emptied 10 rounds from the mag and fired them with no problem from a stock mag. Then fired the remaining 7rds in the Arredondo equipped mag with no problems. I think the new mag spring is too tight. Any suggestions to break it in? Should I load it with 20 rounds and let it sit or is there a better method?