I'm trying to learn as much as I can on this subject of BC variation, bullet to bullet, and have a question for those much more knowledgeable.
Does a highly worn throat affect the BC due to increased wear on the bullet? I'm wondering this due to the idea of obtaining a custom value for a rifle/ammo system, then using said system extensively. Would the BC change with increased barrel wear? Honest question, not trying to stir anything.
My experience has been the average BC drops with barrel wear, and the shot to shot variation within a string rises as the barrel reaches the end of it's life. Both can happen before 100 yard groups open up, but it takes longer than just looking at the throat would suggest.
It's a fundamental problem that limits the usefulness of massively overbore cartridges for ELR.
You'd have to look pretty hard to see it at 1000 yards, but it starts getting obvious at about a mile.
If you want to start evaluating it, it starts with a Labradar and learning to load ammo with single digit SDs. With calm conditions, you can notice some low velocity shots going high, and some high velocity shots going low. You need to be disciplined about maintaining a constant POA and not chasing every shot. Next, you can establish your best bullet and start testing others against it for vertical spread at a mile+. Chrono every shot. I've digiscoped using a spotting scope with a reticle. Saying the bullet velocity out loud while recording makes it easier to figure out when replaying it. Remember that your first impression from this is ES and not SD. Unless you're shooting bench rest, lower SDs are higher scores.
If you try sorting, trimming, pointing, etc. jacketed bullets, it'll help, but it doesn't completely solve the problem. Solids get rid of the dimensional variations, but some of them show very high BC variations. Both of those observations suggest the problem isn't just in the dimensions, some of it is built into the aerodynamics particular to that bullet.
When your first barrel goes south, use more twist in the next one and check to see if bullets with a better BC than your baseline, but a previously unacceptable BC spread, start to work. Next up for me are 7 twists for a 30 and 338.
Some of the consequences of recognizing this issue are you can't perform final bullet selection based on 100 yard groups or how much elevation they take out of the turret.
I'm not a bullet developer or manufacturer. As a consumer, I don't care why, only which product or combination of products performs the best.
