I'm looking for your tips on how to zero a cold bore. I noticed that all my points of impact on my deer are a little higher than what I would have expected. It's pretty much worked out for me thus far, but it didn't even dawn on me until a few weeks ago that I am zeroing in a warm barrel at the range. I marked my cold barrel shot last weekend off my rifle rest and it next shot was 3 inches lower at 100 yards. That seems to track with what I have experienced in the field. All my shots have been at about 120-130 yards and they all seem to hit about 3 inches higher than where I was aiming.

So what's your technique for getting zero on a cold bore at the range? Letting the barrel cool 10 min between shots? How cool does the barrel need to be? Also, do you do a fouling shot? A clean bore will shoot differently than a fouled bore right?

The way I did my last rifle was I went on morning and fired a shot at 100yds. I moved the reticles to point of impact. I put the gun up afor a few hours. Went back fired another shot and adjusted the scope. Put the rifle up for about an hour and moved out to 200yds. Fired a shot. Made adjustments. Waited another hour and verified the 200yd zero. Now I have my own range here at my house so I could do it that way. I would personally give a minimum of 30mins between shots if I could. However my new Tikka will shoot the same point of impact with a cold barrel as it does after 5 shots. I know this because I checked it on several occasions. My lighter weight Savage 110 with the thin barrel will walk after a couple shots. Not much but it does. No fouling shot or cleaning of the barrel when I did mine. I’m not saying this is the right way to do it, I’m saying this is how I did mine.

Shoot, and without moving the gun, adjust reticle to match point of impact. Once the gun is cold, shoot again to confirm. Rinse and repeat.

You have issues other than barrel temp. Id check scope base

Is it just cold bore OR a clean, cold bore?

Clean bores often have a different POI and accuracy than a fouled bore. I have some rifles that I can pull out of the safe and go hunt without issues. Some need 2 fouling shots. I have one that needs about a dozen fouling shots before it will group accurately.

How are you zeroing your weapon? At what distance?
I can boresght a bolt gun from my kitchen table looking at the corner of the living room. Luckily I have a 100 meter range at my camp so I do most of my shooting there. I set up at 25 yards with a rest and fire two shots. If they are consistent I adjust as needed to center, back up to 100, and fire two times. Adjust poi to poa. Test. I should be in the bull by now. If so I adjust the elevation if desired to account for my preferred point blank range.
If I have a number of different loads I may send through a rifle, for coyotes, hog only, target etc, I may test these at the same time and I’ll take notes on any differences in poi. Often these are more or less the same, some have been surprisingly different. I might do this over and hour and a half.

Scope base is fine. Patterns tight. Just that first shot out of cold bore.

Are you cleaning vigorously after sight in? A few fouling shots can actually improve accuracy in a lot of rifles. And if you aren’t shooting corrosive ammo most hunting rifles can go a lot of rounds before needing a patch.

First thing I do is shoot a box of shells as fast as possible and plunge the barrel into an ice chest of dry ice.

I clean it and do it again.

My first 2 cleanings are with a tornado brush and a drill

I clean it then start dialing it in. I then plunge it to cool it off between shots.

Any rifle that doesn’t group one hole at 25 and touching at 100 for me gets sold.

I always chrono, do the ballistic chart and dial it in at 25 yards for whatever MPBR I choose, then I check it at 100 and 200. If its a snap sight-in without a chrono and calc I dead zero at 25 yards with average hunting calibers and its usually good nuff to 250 yards