Two questions, within reason, and knowing this is a long range forum, and assuming optimizing long range means high BC bullets, how can the faster twist hurt? And two, Why are people afraid to twist their new long range barrel using what we know today about what it does for BC's?
Jeff
That's a great question, and I sure don't have the answer for it, but have some thoughts based on my own experience.
I've used both 9" and 9.5" twist 30 caliber barrels extensively for 300 winmag builds (as well as a 30 Nosler, and a few 300 Normas, the winmag is ever popular though). Full disclosure; the 9" twist barrels were mainly rock creek blanks, while the 9.5" twist are from benchmark. I believe the benchmarks to be a better shooting barrel in general, but per their recommendation when I started using them, they suggested 9.5" twist for up to 230's in the magnums as they tend to be less finicky on load development. I haven't quantified the data, but I do know the 9.5" twists have been more consistent for me in load development. Is it because they're a better barrel, or a twist rate difference? Not sure... I'd wager it's because they're a better barrel, but they're input I also put value in.
I've also ran 8" twist .284 caliber barrels in a 280 ackley with a 140 VLD that had zero issues shooting in the low .3's on average. Most would think that'd be overtwisted for a 140, but it shot great and was shot to 1400 yards a few times with success.
One other area of concern might be bullet jacket integrity with high velocity/fast twist barrels. Berger has documented their 338 cal 300 grain Elite hunter bullets coming apart above 3000 fps. Would that be exacerbated with a faster twist barrel or no? Again I don't know... I know for those velocities they recommend their tactical bullet line. Sierras I believe have a thicker jacket as well? You're using lathe turned solids in that 408 aren't you? Be interested to see how production bullets do with that velocity and twist.
You do much more ELR stuff than either I or most of my customers, so I'm curious, how much higher BC are you seeing for a faster twist barrel? Or is the BC not so much the improvement, but the high RPM still happening as bullets go transonic-subsonic keeping the bullet more stable? Obviously BC is changing with difference velocities, I wasn't aware of the BC value actually changing with twist rate as opposed to it remaining more stable at subsonic velocities.
Mike