I own a .260 Rem in a Tikka T3X Stainless Varmint model, original factory 24 inch barrel, 1:8 twist. Weight with Delta Stryker 5-50x56 and Anschutz rail on the forearm, it weighs 12 pounds.
I am using it for target shooting on steel gongs at long range, and paper short range, both using full support with bipod/front rest and rear bag, benchrest or prone on the ground. And maybe to convert to a PRS rifle one day if I want to get into that sport.
About 2400 rounds through barrel so far, and I know the throat has eroded about 0.020" as measured with Hornady OAL gauge and bullets touching the lands. Looks like Tikka bores the throat tight because even with the erosion, long target bullets can still easily touch the lands with plenty of bearing surface to spare, so no limitations there if I wanted to seat to lands, but I don't. I seat off lands usually at 0.010" and more.
Some recent velocity data (using Magnetospeed V3), Six-shots per charge, H-4350, Lapua 136gr Scenar L, Lapua brass fired 7x, annealed (unsure how good annealing was), neck sized, neck expanded with 0.263" expander, primer CCI BR-2, seated 0.010" off lands using ogive and comparator (did not record COAL), seated longer than magazine length, single hand-feeding rounds benchrest style. Charge weights were in increments of 0.2 gr starting from 40.0gr. But I can't post a spreadsheet with it all, so here's a sub-set of 40.0, 41.0, 42.0 gr charge weights:
(Hodgdon website reloading data lists 42.0gr as max load for 140 gr bullet with H-4350).
Charge= 40.0
Mean V0= 2604
Max= 2627
Min= 2592
ES= 35
SD= 12
Charge= 41.0
Mean V0= 2661
Max= 2674
Min= 2647
ES= 27
SD= 10.6
Charge = 42.0
Mean V0 = 2721
Max = 2736
Min= 2697
ES= 39
SD= 14.3
No pressure signs at 42.0gr and I think I could load hotter, but around 2700 fps is good enough for now. Shot at 100 yards in two 3-round groups per charge weight, which on hindsight was a mistake. 3-round groups are not definitive and not really worth listing. I should have shot 6-round groups for higher confidence. But for what its worth, 3-round groups in the full data set ranged from 0.512" to 0.943", and one horribly pulled group at 1.445".
Some recent data below for H-4350 and Lapua 139gr Scenar, Lapua brass fired 6x, all prep the same as above in six-shot charge groups. This time in 0.5gr increments, but I selected a subset for brevity:
Charge= 40.0
Mean V0= 2593
Max= 2603
Min= 2587
ES= 16
SD= 5.5
Charge= 41.0
Mean V0= 2652
Max= 2666
Min= 2638
ES= 28
SD= 9.9
Charge= 42.0
Mean V0= 2703
Max= 2721
Min= 2689
ES= 32
SD= 11.5
Shot at 100 yards. Again I was stupid and shot 3-round groups instead of 6-shot groups. Groups in the full data set ranged from 0.34" to 0.83", and one horribly pulled group at 1.21"
I suspect the neck tension is all over the place. Most of my Lapua brass is now fired 6,7 and 8 times, and I can feel alot of variance when I seat the bullets. Saving my money for an annealing machine, and meanwhile I am increasing my time count on the hand-held single torch method of annealing to see if I can soften those necks to a consistent tension. I recently increased time in the flame to 7.5 seconds spinning it in a drill socket, and using a metronome app for timing.