Mike honestly, Great shooting.
When you're shooting groups, every shot is affected by the wind in one way or another. Most times if you have 4 or 5 flags, the flags aren't all the same condition when you fire, they can be going every which direction. The result on the paper (where the pellet hits) is a combination of all the flags you have and even the ones you don't have or places you didn't place a flag. Knowing that you will never get all your flags to line up exactly the same for all the shots, you take a good enough approach and you get good , great, or bad results. Sometimes you even have 2 pellets go through the exact same hole. In those cases you might think all the flags were the same for both pellets... when in fact if you rewind the tape you see you missed a condition on 2 of the flags. But the missed condition (bad shot) corrected itself and luckily that pellet got blown back into the group...
I'm sharing this Excel file that I use for bullet stability. In the formula we use grains for wt, fps for velocity, decimal inches for diameter, decimal inches for length and if twist is 1:16 you would enter 16... a stabile bullet (slug) is stable at 1.00, and 1.30 is fully stable to the point you cant make it more stable and more twist in the barrel means more torque and more friction. A bullet (high velocity approx. 3000 fps) shoots its most accurate around 1.1 to 1.2 stability in my experience. So I'm trying to figure this out for slugs.
I am not sure how this formula applies with stability below speed of sound though. This spreadsheet will calculate what speed required for a known bullet in a known twist barrel, it will calculate what length bullet is the longest that will be stable in a known twist barrel at a known speed, but most important here, it will calculate what twist you need for a known length bullet at a known velocity. Thinking power in FPE, if i want a 15.5 grain slug that is .266 long, to fall under 20 FPE, I know I need 762 fps so if I can tune the rifle for 760 fps, and use the 15.5 grain slug what twist will be best for this combination? with a centerfire rifle, we can order a barrel in whatever twist we need from a cut rifle barrel maker. I understand most here are hammer forged or button pulled, so tooling would require a specially cut button to achieve desired twist, if it works we're on to something here.
View attachment 1593807912_3879226505eff942803f5d0.77900843.xls 
