Thread: Large MV variation from trueing

Originally Posted by JT_NZ

Sounds like you are doing most things right and I agree that it is a large MV delta from a CAL MV exercise when one has used a CDM. There is the possibility that you are unlucky and have a barrel that significantly degrades the bullet's BC compared to others but lets work through a common fault checklist first:

1. Are you 100% confident that the distance you CAL MV'd at was correct?
2. Did you update your "environment" prior to conducting CAL MV?
3. How many rounds are you using to get your mean point of impact for your CAL MV?
4. What is your MV SD/ES from your LabRadar?
5. How many rounds does the new barrel have through it?

Feel free to flick me a PM, I can give yo my phone number and we can work through it over the phone.

@JT_NZ

1. The one thing I definitely didn't do by the book was the range. I shot it at 657 yards rather then the 10% back from transonic which is about 1020 yards for this rifle. The reason I did this is because its a hunting rifle I wont be shooting beyond 600. I did think this was ok but just means the remainder of my supersonic flight path isn't trued?

2. Captured environment in the shade and without interference from my hands or anything so that should be good.

3. I probably didn't fire enough rounds to get a solid grouping as such but each round fired did impact with the same elevation for the dial applied each time. The difference between first shot and the final trued dope was about 2 MOA hence the big speed difference.

4. Labradar MV was sitting at 2700 - 2720 fps. ES and SD were good throughout most of my load testing but to be fair when I got the final tweak of my loads seating depth I only ran a couple past the labradar as I already had a lot of data in that department so don't have the exact numbers for this exact load.

5. Unsure on barrel count as the rifle is second-hand unfortunately. Its a Tikka T3 though with 1:8 twist.


It shot good and accurate, its the speed that's got me slightly annoyed as I worked bloody hard to develop a load getting the performance I wanted only for the true to throw that out the window haha classic.