I guess we should start with understanding what bounce is in the first place. It is a roundness of the sole, elevating the leading edge of the golf club. This allows for the golf club sole to make contact with the ground rather than the sharp leading edge. I can not send you to a better source than my pal Jeff Summitt. He is a walking talking expert on ANY technical mumbo jumbo having to do with anything related to a golf clubs.
If you want ALL the technical facts about bounce go to Jeff’s Blog entry
Now, from a player’s point of view. Your grandpa’s sand wedge that had a great big bulge on the bottom is no longer what touring pros prefer. Why? For one, the bunkers have changed. Just like putters used to have seven (7) degrees of loft back in the 70′s, now they have three (3) degrees. Our greens today are smoother, faster and firmer, thanks to better grasses developed in laboratories, better mowers, better design etc.
In fact, not only has the putter loft changed but so did the putting stroke. Players today use their shoulders more and use a long smooth stroke where Palmer, Casper and Hogan would pop the ball with their hands. They intentionally wanted to get the ball airborne and then roll.
Bunkers today are well manicured. Sand is soft well below the surface. Where early bunkers could be hard, inconsistent. Golfers were happy to “blast” out of the bunker and get it anywhere on the green. Today golfers are logging “sand saves” and getting it consistently close. Bunkers throughout the golf course are more consistent in sand type, depth and density.
Rather than blasting, players today glide the golf club just below the ball and take far less sand with the shot. No blasting! More touch and feel which is not possible when blasting.
The sand stroke has evolved to more of a lifting and hinging of the golf club on the back swing and then a turning of the chest on the downswing and follow though, holding the angle set by the hands at the top of the back swing. No release or turning over of the forearms with this swing. Quite the opposite. Keep the club face pointer skyward on the follow through.
This strategy would demand less bounce. Plus, if your sand wedge has a huge amount of bounce or bulge on the sole, the golf club becomes unusable for flop shots or any tight or firm lies around the green. The bulge will cause the leading edge to be elevated at impact so you blade the ball across the green.
Here’s a video I did on the bunker shots with some pros on tour. Hope this helps!