Originally Posted by Max Heat
isn't his twist still faster than it needs to be, at the velocities he runs?
I don't have bullet dimensions, and the Matrix site provides nothing useful for information leading to required twist, or basis for BC.
But with a 117DTAC, 7.5tw is not 'too fast' at all.
7-7.5tw is not 'unusual' for bullets of such a high SD, but 8tw would be.
His bullets are cutting round holes at 400yds, which tells me his stability is at least marginal.
That leaves bullet integrity as suspect, given 3moa of broken.
I don't see this as a bullet 'problem' though. There has always been a balance in this extreme(with jacketed bullets) between required twist and bullet integrity. There will always be someone pushing things to failure. For example: Many shooters over the years have shoe-horned themselves into a tiny corner between stability & blowups with 90gr VLDs and cartridges like a 22-243i.
It's nothing new.
Berger went to thicker jackets in adjustment, sounds like Matrix is adjusting, Sierra was already there. But Sierra never pushed bullet potential to this wall -without help, and failures of course.
And nobody really NEEDED to push bullets to failure, or change bullets to compensate. Thinner jacket bullets shoot real well for the rest of us.
Shooters have tried tweaking back on twist rates to drop 'RPMs' below failure. This does not work because of the price paid in stability.
Stability is not tied to RPMs. There is no RPM that equals stable.
Stability results from displacement overcome -by turn of a bullet: 7.5" of a given air density, per turn, barring no other issues.
While RPMs indirectly help or hurt, this has to be qualified by drag resulting from the adjustment, which takes you right back to displacement per turn. A corner..
On the good side, 7.5"/turn is just that regardless of velocity. So it's resulting stability is good/bad across the board, no matter the resulting RPMs.
On the bad side, an excess velocity, at needed twist, challenges bullet integrity due to resulting RPMs.
OP is in this corner.
Ya see what I'm getting at?
Lower velocity, or thicker jackets.