I have the same Cimarron '87' and I bought an extra power Wolff mag. spring. I cut it to 20" and am still unable to get more than 5 rds. into the magazine tube. I then laid 6 shells alongside the mag tube and saw that the only way to get 6 in it would be to remove the spring, follower and end plug. Do I have an extra short mag tube or what? The exposed part of my mag tube is 13.75" in length , measured from the front of the receiver to the forward end of the tube .