I will add my thoughts on this subject. First of all no Doublegun should be "Slammed" shut, leave the slamming to the semi-autos. Bolt wear comes about primarily from rubbing action. Consequently to my thinking the bbbls shoud be closed firmly till they stop & held there as the bolt makes contact, thus not allowing the bolt to rub all the way into its seat drawing the bbls down in the process. As stated if the lever is eased over it may not seat firmly & need to be nudged in with the top lever. When allowed to snap in this is automatically taken care of, but in either method by assuring the bbls are fully seated the rubbing action of the bolt is minimized. "IF" you just close the bbls enough to alloow the end of the bolt to enter the notch & then let the bolt draw the bbls down then rubbing action is "Maximized".
Along this line I currently own two doubles which do not have compensating bolts. One is British, the other German, both are over 100 years old & have double under bolts with a Doll's Head. The notches & bolt are simply parallel to the flats, lever comes to center to a stop, always has & always will. The bolts were apparently made with the minimum amount of clearance to allow them to close. When closed as above described rubbing friction is essentially eliminated. Though both appear well used, but not abused neither shows any appreciable bolt wear at all, as both still lock up tightly.
To my mind it is probably inconsequential whether you ease the bolt in & then seat it or allow it to snap in as long as in the process you "Minimize' the rubbing action. It seems to me that one is more apt to allow the bolt to seat the bbls by the easing in method than by closing the bbls smoothly but firmly & allowing the bolts to then snap home.
