re: Weapons experts chime in on my scenario

I'm not a gun expert - - but I'll toss in two opinions:

1. Unless you've shot a boat load of rounds thru that gun, there's no way the barrel should be worn out after 20 years of hunting.

2. Cold barrel/hot barrel wouldn't explain the difference in POI between first and second shot that you've described. Half an inch to an inch at 100 yards - maybe.

Maybe Kengel will chime in - I'll defer to his opinion on rifles anytime.

Doesn't really sound like a "first/cold shot discrepancy." I don't claim to be a weapons expert, but I've shot a lot of guns through the years, some of which had accuracy problems. This is how I approach the problem. You're going to have to work through a stepwise process to figure it out. Sorry this is long, but that's just how it is.

Based on current info, I'd suspect: a filthy barrel, a damaged crown, a problem w/ the scope (even if is a Zeiss), a problem w/ the rings/base or a problem w/ the action screws. Erratic shots sound more like a problem w/ the scope, ring, mounts or action screws. A pressure point seems less likely. If there's a problem w/ a pressure point, the shots will gradually move in the direction AWAY from the pressure point.

1. Rule out a problem w/ the scope by changing to a scope you already know to be RELIABLE.
2. Remount the base, using BLUE Loc-Tite (NOT red). I always use the $10 Weaver bases, even on my prairie dog handguns. Easy, and cheap enough, to try your rifle w/ a Weaver base. ETA: Before installing the scope base w/ Loc-Tite, individually check the length of each screw. Put the base in place, then screw in a screw into the intended hole. If the base is not TIGHT, the screw is too long. If the screw is too long, cut off the excess w/ a Dremel tool or get a new screw. It should have a minimum of 3 threads for it to have adequate strength. If it doesn't, it's too short and will need to be replaced. Repeat this step w/ each screw in a different hole.
3. Remount the rings. I don't use Loc-Tite on the rings. Be sure the screws attaching the upper/lower rings are equally tightened. If the rings have not been lapped, do so. If you don't have the equipment to lap them or don't feel comfortable doing it, change the rings to Burris Signature Z-Rings (the ones w/ plastic inserts). You can damage the scope by clamping it down too tight in the rings. For example, Vortex only recs 18 ft lbs torque on the rings w/ their scopes.
4. Check for any high spots in the barrel channel or action part of the stock.
6. Check the action screws. Be sure they have the correct amount of torque. Check the 'net to see for any specific tips about the BAR action screws.
6. Use a torque wrench (and follows it's recs) to adjust the mount, rings and action screws. I like the "Fat Torque Wrench" by Wheeler Engineering.
7. Try different ammo. Sometimes a gun barrel needs more than 3-4 shots w/ a particular load before it starts shooting that load well.
8. I don't worry to awfully much about letting a barrel cool down entirely between shots. A well bedded gun should be reasonably accurate even w/ a hot barrel.
9. Be sure the crown is not damaged.
10. Be sure the gun is clean, but use the proper equipment, i.e. a one piece steel rod (appropriate caliber) w/ a good bore guide. More gun barrels are ruined more by poor cleaning technique than by being dirty.
11. Use ammo that's known to shoot well in the gun.

If it's not reasonably improved w/ the above, I bet it's a more serious problem w/ the barrel/action itself. Good luck and keep us updated.

I've had a scope go bad and do something similar to what you described. I would shoot a few rounds things look fine then the zero would suddenly jump on the next couple of shots.