You didn't mention the gun type, bullet weights or anything. Just assuming you would be going with 250 gr in both types of ammo. You could try hand lapping the barrel and making sure the barrel was free floated except for a pressure point a few inches from the end of the stock if a bolt action. This will often settle down harmonics. You can use anything from a business card folded up to a cut down piece of navcon. Ultimately what would be beneficial would be to attach whatever medium you decide on to the stock so it doesn't shift if you disassemble the action from the stock. It will not specifically improve the coreloks but you can often shrink groups in general. I wouldn't want to hunt with a 2" gun at 400 myself. To many variables out in the field and that's just adding to it. You should also know exactly where your first cold bore shot will strike and if a fouled bore is needed to make it more acceptable.
Good luck.