A common error is to have the unit too close to the muzzle. I never use less than 10 feet with handguns or 15 feet with rifles. The instructions may say closer is fine, but I think that's somewhat light condition dependent. Better just to set it back a bit more from the outset.
Take a laser bore sighter to the range with you. Set the gun up with the bolt open, slide back, cylinder open, falling block down, or whatever your gun has as a safe condition. Set the gun up on bags so the sights are aligned with the target. Put the bore sighter in and turn it on. Use the palm of your hand to find the laser and set the stand up so the laser hits your palm in the center of both screen areas.
Go back to the bench and check that the sights are still on the target before you touch anything. If not, adjust them and go back out to check the chronograph position. When it is right, REMOVE THE BORE SIGHTER (can make a mess of both your gun and bore sighter if you forget to).
That last setup procedure answers the question, "how far should my sights be above center in the chronograph screen area?" Using this method you know that when the sights are on the target the bullet will transit the middle of the screen. This minimizes your chance of shooting the unit.
What to do with it? A good beginning project is to go back and get baseline velocities for all your established good loads. Simultaneously you can verify they are still grouping well and don't need to be tweaked further. Having that average (mean) velocity number, if you run out of old component stock and have to change either the primer or powder lot number, you can quickly adjust the load to get the new lots to match the velocity of the old. This assumes the brands and types of component are the same and only the lot number has changed. Matching velocity with a different powder, primer, bullet, or case will not automatically get you a match to peak pressure or barrel time, as these are affected by various characteristic differences of the components, especially of the powder, and are not determined by velocity alone.
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Patron Member