I agree with the others. The drum should not be removed unless it is damaged.
When cleaning the barrel, removing the nipple is about the only thing you need to remove.
As to your question about support, yes, the drum should be resting very lightly against the lock so that the threads don't have to take the impact of the hammer hitting the nipple.
If your drum's nipple is aligned with the hammer when the drum is tight, just use some grease or tape as the others have suggested.
If the threads are not moderatly tight when the nipple is aligned with the hammer and tightening it causes the nipple to swing past it's proper alignment, I would recommend that you go to an Auto Parts store and buy some thread locking compound. It's relatively cheap.
Before you install the drum, clean the threads in the barrel and on the drum. With the lock in the stock and the hammer at half cock or full cock and the nipple in the drum, apply a very small amount of thread locking compound to the drum threads which will be in the barrel. Screw the drum in finger tight, place the barrel in the stock so the drum is seated in the lock (you do not have to install the barrel screws).
Lower the hammer so it is contacting the nipple and rotate the drum until the nipple is square with the hammer face. Then let it set so the locking compound can cure.
This will keep the drums nipple aligned with the hammer for years and will prevent the high pressure gas from leaking thru the threads when the gun is fired.
If the drum ever needs to be removed, applying heat will cause the thread locking compound to loose it's strength.