What die for impact .25

Slug the barrel and send them to corbin!

"Therefore, the first thing to discover is the diameter of your chamber. If you have an existing pellet that fits well, measure it and use that diameter. Or, place a lead cylinder or pellet in the chamber, and use a flat-ended cleaning rod tip on a cleaning rod to compress the pellet and expand it to a good fit, then measure it. If you are concerned about your ability to measure accurately, send five or six sample pellets to Corbin. One pellet might be slightly "off" or get damaged in the mail. Five or six will give us enough to take an average and come up with a useful number for the new die diameter. "

http://www.corbins.com/airgun.htm