I have often wondered that myself. Today especially. I kept noticing that I change my left hand position every now and then from the "pistol grip" method to just holding it "normally" with either the ring or middle finger in the third slide ring. (I still have some personal analyzing to do but I basically figured out that I use the pistol grip when I use alot of the thid slide).
FYI - Stewart Laughton (Canadian Brass) plays with the pistol grip. (Watched him play the other night and I don't think it changed through the whole concert.
Another thing to check out would be the Alexander technique. I've never had a sesison but apparently they look at how you play (any instrument) we're talking posture, hand position, pressure everything. They look at how you play and see where the tense areas are and offer suggestions on how to fix it or it may become a problem in future years.
http://www.alexandertechnique.com/
good luck
Eric S.
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Eric Sproul
Practice is like filling a leaky bucket
Bb: Yamaha Xeno 8335
C: Bach Stadivarious 239L and 25A leadpipe (Owned by Eric Sholtz)
Flugel: Yamaha Bobby Shew 6310Z
Mouthpieces: GR tech
www.stadband.ca 