Go to the range and duplicate the conditions of the hunt. This means similar distance, how the gun was held or braced or lack of it, load ect. Try shooting and see if the weapon is still sighted in and shooting like it was. Try to isolate if it is the rifle, scope, load or the nut on the end of the handle.
Classic case is a friend who had a Savage bolt action .243. Off of sandbags, from a bench, he could shot groups that were one ragged hole at 100 yards. He sighted in the rifle 1.5 inches high at 100 yards and put it away until hunting season. During the first four days of the 2002 season he missed or injured and lost 3 deer including one fine buck. He offer to sell me his POS rifle at a big loss but I convinced him to go shooting with me on a morning we could have been hunting. After he put five rounds into a dime sized group off of a sandbag rest he was stratching his head. I pulled his tree stand off of his truck and mounted it about 2 foot off of the ground on a nearby tree and invited him to repeat the group. Out of five rounds he only cut paper once. Frankly, shooting off hand he could not hit the proverbial broadside of a barn. We installed a homemade rifle rest rail on his stand padded with pipe insulation foam and he shot decent groups from his new setup before we quit that afternoon. As luck would have it he did not see another deer until the next year but during the 2003 season he took two bucks and a doe. Most importantly he did not miss or injure and lose any deer he shot at.
First thing to check is the scope and mounts.
Lose mounts and/or rings are easy to find and fix.
A defective scope can be a pain to diagnose and a shifing zero can depend be hard to isolate...try another scope.
Of course if you really isolate it to the barrel or gun then you have to ask why? What is inconsistent?
Lock up?
Is the twist stabilizing the bullet weight you are using?
Are your groups stable at the distance you are shooting?
Hay this half the fun or so they say.
LOL