Gun fit is a bitch and the more adjustments you have, the more chance you will probably be wrong in one way or the other. Rifles are not shotguns but there is an analogy to the good fit of a shotgun and a good fit of the rifle to you.
I have much more experience with shotguns than I do rifles but my procedure with adjustable stocks is pretty much the same for both types of guns.
You need to have the gun in a position that will allow your body to be as relaxed as possible with the gun firmly in the shoulder socket, the cheek and eye relationship to the sight such that your neck is under no strain to reach a natural position, looking through the sight and your head is upright with your eyes level and your neck leaning neither backward or forward. Got it? Good.
How to get there.
1. Without adjusting a darn thing, raise the gun up and set the butt plate/pad firmly in your shoulder socket, left hand near the balance point of the gun, right hand on the grip with the trigger finger extended and outside the trigger guard. You should be in a standing position for this. we'll get into bench and prone and position shooting later.
Where is your head? Where is your right hand? Do you need to crane your neck down to have your cheek firmly but not pressing on the cheek rest? Raise it and remount the gun. Better? Good.
Is your right fore arm roughly 90 degrees to the gun? Elbow about even with the grip. Lengthen or shorten length of pull until you are there. I actually find I am more comfortable with my elbow about mid way between the point of my shoulder and the grip, it keeps me from pronating my wrist and I have a damaged rotator cuff which makes getting square a bit painful for me. Pain is bad.
OK, play a little with that pad height so the gun is back in that shoulder socket. It is important to managing recoil. Arms getting tired from lifting the damn gun? Go take a break. I never said this was gonna be easy.
2. Once you have the rear of the stock and the natural height of the cheek weld established, mock mount the scope, just snug everything now, the torque wrench will come out later. Center the turrets between the rings and pick a notch for the rear ring where you can see the whole field of view in your scope. A buddy or understanding wife/SO is handy here. Loosen and snug and loosen and move and snug until, with the gun mounted, you are seeing that nice bright circle and it doesn't go away when you move your head back and forth a bit. Scope should be in the lower half of the magnification range if it is a variable when you do this. It helps to be pointing it out at the sky (scares the neighbors some) but a white wall will do for now. A bipod and a rear bag can help a lot with this as the gun is gonna get heavy again otherwise. Snug the rings a little more when you get there. If the vertical seems OK but you are struggling with the view of the scope turning into a vertical ellipse see if you can move the cheek piece left and right. Some are adjustable, some are not. If you got squirrel cheeks you might need to shave it a bit, thin face you might need to move it left a bit. You did remember to measure the height between cheek piece and stock, right? Slipping part of a deck of cards between the vertical posts until it is a tight fit will allow you to return to the same height. You'll probably have to remove the cheek piece to make the horizontal adjustment. On my gun, a 45ACP case is just the right height laying on its side. Makes it easy to slip one into your range bag.
3. Make the final fore and aft adjustments to the scope by sliding the scope a little in the rings. Now is a good time to adjust the ocular so that the cross hairs are in sharp focus. Scope needs to slide freely in the rings and now would be a good time to torque the rings or, if you are using a 1 piece mount, the mount to the rail. BTW, you only want the mount on the receiver portion of the rail, don't let the mount or rings bridge over into the hand guard. Check that the scope still slides freely in the rings with no binding.
4. Now is the time to bore sight the scope, set parallax for your first shot and make the rifle go boom. You are probably going to want to tweak all of these adjustments as you see how the gun and your body position react to recoil, whether there is strain anywhere in your body as you mount the gun and adjust as needed. Here is where shotguns differ from rifles. All of the above, with the exception of the scope is the same on both rifles and shotguns. On a shotgun you regulate the stock so the shot pattern goes where you are looking without having to put any strain on your body
With a rifle, you do the same thing but you wind up with a relaxed body that allows you to look directly down the scope with no strain other than that necessary to support the gun. The rifle uses bone on bone and body on ground to steady with shifts of the entire body to handle aim.
5. The rest is body mechanics and practice, practice, practice.
Best tip I can give you is find and experienced coach who will help you with gun fit and body position. Without either, your gonna send a bunch of rounds down range to no avail.
