Not only is it in the technique however.....
Aside from debating if the slap shot is an integral part of the game or not, for a forward (which I believe it is), I'm sure some of you guys wouldn't mind maybe a suggestion as to a possible reason why their shots are not as hard as they'd like?
Could be the stiffness of your stick......
How many guys in here use a stiff flex shaft/stick? Probably a good majority, right? The stiffer the stick, the less chance it will break on a hard shot, etc..
But if you think about it, the hockey stick is designed with flex in mind, so that the 'kick' of the stick is what gives the puck huge velocity.
Try playing with a stick with more flex. My first TPS Response I had bought was a stiff flex. HATED it... but I had always used a stiff flex, and didn't think of possibly using anything else. I'm about 6'1, 190.... not too big, but I figured that I'd snap anything less than a stiff.... I had talked to a friend, and he suggested trying a regular flex to help with my slap shot (which was pretty good with the 95 FLex Easton Z-Carbons I had been using (as well as breaking))
Slapshot fixed. Came off the stick twice as fast, I had more control.... you could feel the difference, and it was quite a bit.
Then I got the crazy idea, and bought a Whip flex (which would be about a 90 Flex Easton)....my shot has never been harder. The stick flexes like crazy under full load, but won't break, and the release is just insane......... might not be the problem, but it's worth a try