If you are new to shooting off the bench, you may not know that setting up the rests plays a significant role in accuracy -- "significant" here meaning tenths of inches, not hundredths. Some things I know; some I only suspect, & Iíll try to keep them separate. If anybody can confirm or deny the guesses, that would be great.
When you set up the rests, the gun should be fairly free to move. I believe (from Vaughn) the bullet clears the barrel in about .1 inch of movement, so weíre not talking as much about movement of the rifle as about loads placed on the stock & transferred to the action & ultimately the barrel. I do know that if the rifle wonít "track" it likely wonít shoot, even though this tracking is probably only evidence of loads placed on the stock.
The first thing is mechanical; the sand in the front rest should be evenly distributed in the bag; you can use a small piece of wood to get it flat. Donít assume it will always remain so, it has to be checked from time to time. I know this applies to the Bald Eagle/Protector style of front bags; it may not apply to the Hohen windage top, where the sand layer is quite thin & has multiple pieces of metal restraining the sand/bag. (Hint: NBRSA & IBS have ruled this top legal for conventional group & score matches. It is usually NOT legal in 1000-yd competition, where we take the "1/2-inch of sand" rule seriously.)
Tracking is hard to define, but pretty easy to observe. Set the rifle up in the rests, align it on the target, & pull it back and forth a few times, while looking through the scope. Push and pull with your hand, donít pull back with your hand and push forward with your shoulder. The crosshairs should move up & down in a vertical line; not at an angle or circle or a jitter. By the way, the number of people who can successfully push a rifle back with their shoulder during firing a string is quite small. Use your hand to push it back, or if you canít stand this, practice using your shoulder until youíre one of the few.
The second check on tracking is that when the rifle is moved back and forth on the bags, the crosshairs should return very closely to the original aiming point.
Both these things should be checked before firing, but should remain true when firing. If they arenít happening, check the position of the rear bag. When I set up my rear bag, I lift the rifle so it will clear the ears, & wiggle it slowly left & right. The centered position, where you feel the least resistance, should be right over the groove in the rear bag.
So, the basics are that the rifle should "return to battery" in the bags after firing a fair percentage of the time, where "ďreturn to battery" is defined as "returning to the aiming point" rather than the more conventional "physical position of the barrel." It should also do this in a straight line, with little jittering. You wonít get consistent RTB with sandbags, but it should happen, & if the bags are properly set up, it wonít take much to get you back to the aiming point.
Generally, the end of the stock is not a good place to put the rests, particularly the front rest. I recently put a wood stock on a 1000-yd rifle. During the finish sanding, I cheated & used a vibratory sander. There were places on the butt and fore end where the sander would make the whole stock vibrate, & other place were this didnít happen. With this stock, the places where the
whole stock vibrated were near each end. Likely, this would be a lousy place to have the rifle riding in the rests. It might be worth while to take a vibratory sander WITHOUT sandpaper in it & go over your stock, looking for places where the whole thing seems to resonate -- you might want to pull the scope before trying this. If you find any, Iíd not have the rests in contact with those places.
Holding a rifle on the bench.
Most books & most people tell you to shoot free-recoil. Great when it works, but it doesnít always work, particularly when you double with the guy on the next bench. A light hold is usually described as a little thumb pressure with the trigger hand, applied straight down. This can be hard to do with both consistent pressure and good trigger control until practiced.
An alternative is to apply pressure with the non-trigger hand. The easiest way to do this is to hold the fore-end, then relax your arm so that the arm does no steering, but simply adds itís weight to the rifle (in a downward direction). The big disadvantage with this technique is that it is slow; the non-trigger hand now controls only the vertical position of the rifle; any horizontal change means moving your hand off the fore end to adjust a windage top. Squeezing the rear bag is out unless you have three hands. The technique is most useful in determining whether or not your rifle shoots better with pressure added when youíre not used to adding this pressure, or when testing a moderate kicker.
More generally, "holding" the rifle should in no way be construed as any form of steering the rifle. "Holding" a rifle shot off the bench is more akin to shooting a pistol than what most people think of in "holding" a rifle -- In shooting a pistol, you move your whole arm or even your feet, your donít steer with your hand. I believe that if you hold a rifle at the bench with the trigger hand (except for a little downward thumb pressure on the comb), the hold should be pulling the rifle straight back into your shoulder, just like the fingers pull a pistol back into the heel of your hand. Any side-pressure will result in shot dispersion.