I find that one of the main problems that shooters have when shooting off of the bench with ARs is that they work from the grip forward, rather than establishing finger position first. The most important thing is that the direction of trigger pull be correct, not that the trigger hand be comfortable.
In short range benchrest, thumb hole stocks are long out of style, primarily because if you have your whole hand in contact with them, you will tend to torque the rifle as you pull the trigger. For this reason, for rifles that are held, because of stock design, rifle balance, recoil, and other factors, I suggest that shooters apply rearward pressure with the second and possibly third finger of their trigger hand, and not the little finger.
On cheek pressure, for shooting from the bench, I like to use rings that are tall enough so that I can keep my face off of the stock as I aim and fire.
The other issue that is commonly done incorrectly is to have the front bag too far forward on the forend, letting the bag position be determined by a rests forend stop, and not experimenting with position over a wide range. If you are holding a rifle you do not really need to be concerned with how it balances on the bags to the degree that is required if you are shooting free.
The same thing that I wrote about ARs applies to vertical grips as well.
Some time ago, a friend was shooting a tactical stocked custom rifle and not seeing the results that he wanted. I moved the front bag back to the middle of the forend, lowered his cheek piece until he only had very light contact with it, and had him only use his second and third fingers on the grip, positioning his hand so that he was pulling the trigger straight back with the middle of the first pad of his index finger. I cautioned him not to push down with his thumb, and to pull the rifle into his shoulder with moderate, and consistent pressure. His groups shrank to half of what they had been.
I find this sort of effect from making changes in how a rifle is supported and held to be quite common. Shooters who have years of experience tend to think that they know how to shoot, and that all that they need to do is try harder. In many if not most cases, they need to "try different".
Doing something wrong for a long time tends to impede their progress, and even after I have helped them improve their results, I find it very common that they fall back into their old habits, when observing from a distance during subsequent range sessions. For this reason I think that when one finds a method that works better, that shooters take notes, and review them from time to time.
In my experience, most rifles produce better results when they are held, unless they are specifically designed for shooting free, and the bags and rest that are used are of that type as well.
