Ddid you do a very accurate velocity check both before an after that cone lengthening. "IF" it reduced the recoil then it is about 150% Positive the reduction was due to a loss of velocity. As Eightbore said the same thing can be accomplished by a lesser charge of powder, which saves a few pennies rather than having to be paid for.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra