I think both the Mountain (from what I hear) and Bob's (from experience) are good bolts. I like the looks of Bob's better, not that it matters much.
The old Mountain bolts were very, very light, and minimized any kick. I hear they didn't play very nice with the LP mod, and were not a "drop in" part since LP and HP pressures needed adjusting to get it all set up. The new ones weigh about same as Bob's. Although these aftermarket bolts are lighter than stock, its not by much, and it only reduces kick a little bit. The good part is that they won't wear the anno off of the inside of the gun.
I have experience with early Mt. bolts and Bob's bolt. The early Mt. bolt I had worked horribly. The face of the bolt was machined out too large and caused the paint to sit deeper in the bolt causing issues with the eye. The bolt was also too light and caused tuning issues. No experience with the new Mt. bolt. Just ended up getting Bob's. Can you say plug and play.
Alright, THANKS A LOT GUYS! This really helped. I'll get Bob's bolt. I think I'm going to make mine completely Bobized. Like the bob bolt and get a bob power reg; Not to mention that my timmy is a bob long one. heh. Thanks again guys!
Might want to search for some older threads on bolts. The MntPaintball delrin has gone through multiple improvements and certain models work better with LP mods while others work better with the stock configuration. The gen5 Mtn delrin has a tighter fit than Bob's so you can get (at least theoretically) better efficiency, etc.
Neildepainter from MntPaintball has tested all types, to include Bob's, and probably is one of the better sources of information on the pros and cons of each bolt.
I have a gen 1 MtnPaintball delrin but am using Bob's delrin with the open face currently since I converted to the LP mod. I really didn't have any problems with the Mtn delrin that I didn't cause myself by poor paint/barrel selection. I really haven't tested them side-to-side, though, nor have I tested the more recent Mtn delrin creations so I can't give you a comparison. On the plkus side, Bob's came with both the open face and venturi delrin bolts and the bolt pin was already installed in the open face one so I didn't have to switch it out of my older bolt.
"If we measured rof in $/min instead of bps, more people would play stock."