What caused velocity change, and which velocity to use for dope chart

[Unknown]

The other day I was shooting a couple of Grendels, and got the following results:
Load:
123 grain Amax
30.2 grains of W/748
C.O.A.L. 2.260
CCI 450 primer
Lapua case

19.5 inch Shilen barrel was cleaned with Sweet's 7.62, the sweets was neutralized, then the bore was coated with Kroil that was removed with about 5 tight dry patches.
2495 fouling round
2528
2543
2568
2558
adjusted sights
2571
2568
2552
2561
2599
adjusted sights
2535
2568
2566
2565
short break
2501
2451
2484
short break
2484
2488
2494

Discounting the fouling round, there are 19 rounds. Average for the 19 rounds is 2560. Average for the last 6 rounds is 2536. Am correct that the barrel is settling down after it became re-coated with some copper and therefore, I should use the velocity from the last six rounds, or would I be better off taking the velocity of all 19 rounds? If I split the difference between the two groups (24 fps), I could add 12 fps to the 2536 fps from the last 6 rounds, and use a velocity of 2548 fps.

What would you do, and why?

The same load shot out of an 18 inch Lothar Walther barrel that was only cleaned with Kroil, and not copper stripped:
2414 fouling round
2449
2437
2461
short break
2438
2433
2440

It sure looks like the barrel that still had copper in it gave more consistent results...especially the last 3 rounds. I would presume that is the result of all the Kroil finally being burned out of the barrel.

Any input will be appreciated. I'm just trying to figure the best velocity to use for a dope chart.

 

[Unknown]

When I took the breaks, I never left the stool at the bench. There may be small changes where I shoot through the chrono screens, but my targets were at 100 yards, and in order to get relatively decent group sizes I have to be pretty consistent. The 100 yard targets weren't more than 12-16 inches apart, so I don't know if this would account for the velocity differences.

It seems that my speeds seemed to go down a bit as the barrel heated up. In the next to last group with the Shilen barrel, velocity spread was 81 fps, in the next group, velocity spread was 7 fps.

When velocity went down, so did extreme spread...But 3-4 shots isn't too much of a sampling to base an overall outcome on.

I think I'll just use the 2548 fps velocity. The local practical rifle matches on steel go out to 535 yards. The elevation drop difference between the 2560 and 2538 at 535 yards is only 1.7 inches. If split the difference and use 2548 fps as my operating velocity, I'm only looking at an elevation difference of .8 inches either way at 535 yards.

I would be VERY thrilled if, (from true field type shooting positions,) I could actually hold good enough to see whether I was shooting .8 inches high or low. Atmospheric, or environmental differences can make more of a difference than that...