Ken: Peeling motor is something that shouldn't be done period. Light sanding with 220 to remove the aft mushroom "burr" is perfectly safe as long as it doesn't take of too much The slight swelling on the propellant end is I'm told by Estes is in fact caused by the ramming process in manufacturing. Nearly All Estes motors will have this slightly larger OD on the area of the motor containing propellant. Generally this aft end swelling won't cause a problem with standard BT-5, BT-20 and BT-50 size Estes Standard size motor tubes. Several have mentioned Wood glue shrinking of centering rings this can cause very tight motor tubes. What I've done in the past to correct most Tight MMT tubes is to use a 1/2" wooden dowel to gently enlarge the tight 13mm (BT-5) motor mounts, 11/16" dowel for 18mm (BT-20) mounts and 15/16" dowel for 24mm (BT-50) motor mounts. This process is a little harder if Estes metal motor hooks are present but it is possible to gently stretch the inside of the motor tube to easily fit the motors without splitting the tube. apply to much pressure on the tube ID can split the tube so progress slowly.