Hmmmmmm
. Thats strange alright.
The first thing Id check would be to insure your Tikkas barrel is still floating. My Godson just got a Tikka with the beautiful walnut stock and roll-over cheek piece
and I ran a rather heavy piece of paper down the barrel and between the barrel and the barrel channel on the stock. It went easily and didnt leave ANY doubt that the barrel was free-floating. Yours should act the same way.
Check it while the barrel is COLD, then check it again when the barrel heats up. It should remain free-floating all the time. If you find it is NOT floating, then remove the barreled action from the stock and wrap some sandpaper around a wooden dowel that will fit into the barrel channel on the stock and remove more of the wood where you find the paper catches when you check the barrel for being free-floating. If you do any sanding, youll have to cover the raw wood with a clear plastic coating to insure moisture doesnt get to the raw wood and cause it to swell up when theres a lot of humidity in the air or if rain gets down into the barrel channel. Your dont need to lay on a thick coating, but you must be sure you cover & seal any raw wood completely before re-installing the stock.
As far as shooting groups
a rifle with a free-floating barrel should shoot to the same point of aim regardless of whether the barrel is warm or not. However, you should NEVER keep shooting your rifle until the barrel is HOT.
First, Id recommend you use 3-shot groups rather than 5-shot groups since your Tikka is a HUNTING rifle
not a bench-rest rifle. Youll probably never get more than 3 shots at any game animal, so its those first three shots that will either bring down your quarry or not. So theres no point to shooting 5-shots.
Second, Id recommend you fire ONE SHOT, then wait until the barrel is at least cool (if not cold) before firing another shot. I suggest you do this consistently when firing your 3-shot groups. Therefore, one 3-shot group shouldnt take more than 10 minutes or so to complete the two 5 minute breaks
one between the 1st & 2nd shot
and another 5-minute break between the 2nd and 3rd shot. Your Tikka should easily shoot LESS than a minute-of-angle (less than 1 inch at 100 yards).
Frankly, I have gone to shooting in my hunting rifle groups at 50 yards
and just checking them at 100 yards to insure they are the proper distance above the bullseye at 100 yards. Generally, for a modern high-powered rifle, that will be about 2½ inches above the bullseye @ 100 yards which will yield a point-blank-range of about 260-300 yards depending on caliber. For your 7mm Rem. Mag. using 160 grain Nosler Partition Bullet with a ballistic coefficent of .475 @ 3,000 fps, my ballistic program indicates the following:
25 yards = + .10 inches
100 yards = + 2.58 inches
150 yards = + 3.00 inches
200 yards = + 2.23 inches
250 yards = + .22 inches
254 yards = ± 0.00 inches (dead on)
275 yards = - 1.31 inches
300 yards = - 3.13 inches
This gives you a point-blank-range of approximately 295 yards wherein the bullet never rises or fall 3 inches above or below the line of sight (aka point-blank-range)
Good Hunting
Ron T.