Some production rifles are made so getting the drum out without destroying it is nearly impossible. I don't know if they did it on purpose, but it seems that way. I would try with normal pressure and if it won't budge, just inspect it as good as you can and get a oversized nipple from Track or several other companies. I had a similar problem and I just cleaned out the old threads with penetrating oil, picks and .wire .22 brushes. I then ordered two of the oversized nipples that my uneducated guess led me to. I found out what size the nipple was by measuring and trying it on a thread gauge, then I used a caliper to measure the inside threads and the nipple threads. The new nipples in my case were called a .030 over 1/4 x 28, which made them a .28"x28. The new sharp threads went in very slowly with alot of oil and back and forward motion. It actually "freshened up" the old theads and took up the slack from the removed rust. Mine was on an old Belgian shotgun, but if yours is a modern production gun it might take a metric nipple. They make them oversized , too. Do your homework first!