sounds like it is stuck on the center hub. lube it up & whack it.
I'm in agreement with the above assessment.
IF you had to tap on the drum to get it to seat, then it is probably stuck on the center axle hub. All the hammering and beating on the drum from the inside lip outward will just tend to worsen the situation. I believe that the lip on the drum is "digging" in to the outer diameter of the hub.
I've had success by evenly heating the outside face of the drum (near the drum/axle hub interface) in a circular motion to expand the drum slightly so that it will slip off of the hub. I've used an oxy/acetylene torch to do the job but I believe that you can get enough heat with a propane torch. I've performed this process several times and each time the drum literally popped free from the hub on its own when it was heated sufficiently.
Once that you have removed the drum, lightly file/sand the sharp edge off of the drum so that it doesn't happen again. If needed, enlarge the inner bore of the drum by a few thousandths to allow the drum to "freely" slip over the hub.
It worked for me.
Frank