On the 500 (unlike the 590), you DO have to unscrew the mag tube from the receiver. The barrel-lug end plug is permanently attached and should not be messed with. Most mag tubes have Loc-Tite on the threads where they screw into the receiver. On mine, I took a propane torch and CAREFULLY heated the receiver until the Loc-Tite broke loose and was able to unscrew the mag tube with very firm hand pressure. Don't get the aluminum receiver too hot!. Just heat it up til the Loc-Tite breaks loose. It works. To save trouble the next time, I didn't bother puting Loc-Tite back on the threads when reassembling. The tube can't back out with the barrel on anyway.