I get that, but he covered the quality of bullets and the old mindset. As noted, a few of us here have shot 1:7" .25 cal with 110/115 cup and core bullets without any issues. What you do with the information is entirely up to you.
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Super Fast Twist Barrels for Hammer Bullets
- Thread starter nksmfamjp
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Longrangers
Well-Known Member
Ok
I know in my benchrest guns when I go to a faster twist they shoot ok but I go to a little slower twist they grouped better and if I went slower yet they shot ok. Seems like there was a happy medium.
Yes, Sir!
Out of curiosity was the reduced max speed the only detriment or was there other issues that arose? I went with a 7 twist for my 6.5 PRC and the 8 twist for a 30-06 thinking that the increased twist would provide additional terminal benefits at lower velocities due to the 18" and 20" barrel.
Longrangers
Well-Known Member
So if I go with a faster twist and they don't group as well what is my benefit to going to a faster twist unless I shoot strictly monos? Just curious.
The primary purpose of barrel twist is the gyroscopic stability of the bullet you will use, whether a mono or cup and core bullet. Bullet manufacturers often have a minimum barrel twist recommendation.
I was pushing for 5K with a 50g bullet and the twist is what hindered me, I know this is gonna sound at it I could actually feel it the harder I pushed.
Other than that it shot great.
Had I went with the 9 twist I would have made it
For what it's worth, Applied Ballistics did a test years ago on twist rate and its effect on muzzle velocity. Here's an excerpt of their findings:
bulletin.accurateshooter.com
How Muzzle Velocity Changes with Different Barrel Twist Rates « Daily Bulletin
Many barrel-makers mark the twist rate and bore dimensions on their barrel blanks. Does muzzle velocity change with faster or slower barrel twist rates? Absolutely, but much less than you might think. Faster twist rates do slow down bullets somewhat, but the speed loss is NOT that significant.
Longrangers
Well-Known Member
So I guess where I'm at is if I was shooting a Sami spec cartridge I myself would not get a faster twist just in case say like on a hunting trip you ship your ammo and firearm and ammo gets lost and you have to fall back on factory ammo. I do shoot CEB's out of a 338 but my twist is suitable for their bullet and jacketed bullets.
Your S/F will climb with a faster twist with either bullet
I've seen a lot of people try to blame twist rate as the reason they got poor groups/accuracy (not trying to be disrespectful by that) whether it was too fast or too slow of a twist rate. But when you calculated their SG, it was with requirements. It's only human nature to try to find something to blame when things didn't go as expected. We struggle sometimes finding the true culprit.
So in reality, the issues come from something else. Typically it's either imperfections in the bullet that the high rate of spin exacerbates (inducing an imbalance in flight that can either throw off accuracy or rip apart the bullet), not being in the right powder charge node, not being in a seating depth node (jump to lands), etc.
Changing rate of twist can change how the bullet engages the rifling and tuning powder charge and seating depth is usually needed. Factory cup and core ammo is typically tuned for more typical twist rates, if that makes sense.
More aggressive twist rates tend to foul more and at a higher rate too, and that can negatively affect things. The list goes on, but my point is don't worry about using a fast twist for certain monos and then not being able to get good results from good cup and core bullets with it too. You just may need to do some tuning is all.
I have done seating depth node tests with success on factory ammo and hootenanny better groups. The many different barrel tuner and tuner brakes out there can really help with this sort of thing too.
That would be a wise decision IMHO
I had some 115 VLDs not make it to a 300yd target. But launch speed was close to 3,900 out of a 30" 10-twist 25-300 RUM. I think it might have been due to the lead core in contact with the copper jacket turning molten at my MVs?
What are your MVs with that 7-twist Weatherby? ~3,500?
You are probably correct. A 30" barrel at those velocities and likely older thinner jacketed VLDs all worked together to produce a ton of friction, heat, and melted the cores and caused the bullets to either come apart or yaw so badly they flew all over the place.
Long for caliber (lots of bearing surface) bullets, thin jackets, pure or near pure lead cores, fast twist, long barrel, and any combination of those can definitely lead to issues.
So while twist rate alone won't affect accuracy or velocity that much as long as SG is within parameters, other factors can negatively affect the end result. It just depends on certain things and the extremes.
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