Jonathan
Sorry to hear that your first experience with the new rifle were less than anticipated.
First thing I'd do is sit down and recreate the days events.
What did you do differently than when you were shooting the older rifle?
How many NEW variables were involved?
Did you clean the rifle before shooting it?
Did you clean it between different ammo types?
Did you check the action screws tight? Loosen and then tighten rather than checking for tightness only.
Is the barrel touching the stock anywhere? Check the underside of the barrel too, use some folded paper to check clearance around the barrel.
Were you shooting from a bench and front rest? Did the front (or rear) sling swivel come in contact with the rest(s) or bags during recoil? Did the shooting position cause the barrel to touch anything, including the inside of the barrel channel?
Do you get a good cheek weld or is the new rifle ill fitted to your eye height?
Examine the fired brass. Anything abnormal about it, compare it to unfired rounds. Check for runout on the fired and unfired brass. Is the fired brass 'egged' on the body, or neck? If you don't have a runout guage, slowly roll the fired round across a clean, dry, flat surface and watch for 'wobble' or any out-of-roundness.
Check the crown of the rifle, there should be no nicks or unusual markings.
Open the mag. well and check the mag. box loose (it should be loose enough to move with your fingers). If it's bound up tight it may be caught between the floorplate and the action.
Check the scope, mounts and bases tight. Did you install the scope, bases and rings or was it assembled by someone else? If you're not sure about the optics system, remove everything, scope, rings and bases. Reinstall the bases, only install one base screw at a time and then check the base for tightness. If the base is tight to the action with only one screw installed, loosen that screw and install another screw and check for tightness again. Repeat this procedure with each screw and base hole... each screw MUST be able to hold the base tight to the action on it's own. Once all screws have been checked, tighten all the screws and install the rings. Check the rings for fit and tightness too. The rings should only contact the base and not touch the action.
If it still won't shoot well.... let someone else try it (preferable a good shooter). Don't 'front load' the other shooter, in other words, don't tell the 'test' shooter that you can't get the rifle to shoot and you would like him to test it. Just have him shoot it sort of as a 'how do you like it' test. If it shoots poorly for him too, I'd say it was the rifle and I'd continue trouble shooting the thing or consider a custom barrel fitting or get rid of the thing.
There's nothing more irritating to me than a rifle that won't shoot, with the single exception of a visit from my mother-in-law
.