In instances that I am curious I start looking at published load data some will say what gave the best accuracy with your bullet weight and which ones gave the most fps. I tend to go with the fastest fps powder but if the most accurate is close to the fastest I opt for it. Do some research it's good to learn about your round and in this day and age of powder lack of supply what you can get for it.
Fast rate of twist?
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264WM
Well-Known Member
Mine is a 264WM with 1 in 8 twist shooting a 85gr HP (Sierra) at 3827fps so what is the rpm. This is out of a Shilen 30" heavy varmint barrel.
344,430 rpm
The formula to calculate a bullet's RPM is equal to Muzzle Velocity (fps) x 12 inches x 60 seconds / Twist Rate (inches).
3827 x 12 x 60/8 = 344,430 rpm
Can't imagine many of those hold together. If I remember correctly that bullet was designed to work at mid range velocities. How did you decide on that load in a .264 Win Mag?
HARPERC
Well-Known Member
We've learned a lot from BR competitions, not all of it applies to hunting.
One has to look at a specific bullet in specific cartridges for specific purpose.
One of the BR bullets I looked at online (Can't recall brand) was recommended at 2700 fps or less.
Hunting (big game) we're chasing terminal performance, we'll take any improvement in accuracy, but not many hunting style rifles are capable of BR groups.
Several have tried to overspin, Hammer bullets at hypervelocity, and have yet to find an upper limit for either.
If you get a chance pick up PO Ackley's book #1 where he addresses the subject of killing power using the .220 Swift and .17 caliber as examples. He very much believed in high velocity and bullet rotation, in a fast twist barrel as two key factors in killing power, as did Roy Weatherby. Good luck. Cheers
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The proper twist rate for your bullet is how I roll. If the twist is much faster than my bullet, the bullet may not "go to sleep" for 200 yards, in which case the Bullet Yaw decreases that BC.
Much work has been done to get a bullet to go to sleep as quickly as it can out of the barrel, eliminating as much bullet yaw as possible.
Twisting the fastest rate possible due to the fact that one day you may wake up and decide what you really want drives you to shoot heavy for twist rate bullets, whether or not you want to go there or not.
For example, when I want to shoot 140g-150g cup and core bullets in my 7 mags and 7 sTW, I shoot an 11 twist and three grooves. This is going to drop pressure while boosting velocity. The same thing applies to 30-cal hunting bullets, you slow the RPMs down, and they penetrate better, so lighter bullets perform in some respects like heavier bullets.
All of the twist rate recommendations are steeped in Traditions, but when you start actually using a twist rate calculator, the learning curve is quite impressive. The Berger Bullet website can give you a glimpse into what is necessary on the twist rate for a particular bullet.
Very fast Bullet RPM makes bullet jackets open up faster(316,000+), we have seen this over and over again on varmint rigs. So, do you want your big game bullet to blow up quicker in an animal, then twist if faster? This may also introduce bullets blowing up prematurely, especially in barrels with cracking in the bore and rough finish due to heat/ pressure.
In the 6.5 caliber, the 147g and in the 7mm, the 180g eldms are famous for blowing up when twisted too fast or shot too hard. The Engraving pressure as the bullet enters the lands is tremendous with the pressure spike that accompanies it, and controlling bullet base deformation is critical.
Berger had one heck of a time with his first 6mm 105's when they came out due to boat tails deforming during obturation as pictures taken by Bill Davis at Aberdine Proving Grounds showed. They changed the alloy mix which cured the problem-Olympic Comp bullets.
In the 22 caliber, 6.5 twist is needed for hot weather with 90g Bergers, and throat accordingly, which means the use of lighter bullets you should consider a crap shoot.
Prudent to take a step back, Use a ballistics calculator, plug in your bullet, velocity, and temp, and see what gives you a 1.5 stabilization factor, with a 1.2 being marginal during certain weather and elevations. When shooting hot rod cartridges, I always use a slower-than-normal twist, I am looking for that magic RPM rate that I want given the velocity of the cartridge, elevation, temp, etc.
I do not shoot monos as a rule with the exception of 110g Barnes ttsx in my 270, 80g ttsx in a 257 Weatherby, and 80g TTSX in a 243 win.
Much work has been done to get a bullet to go to sleep as quickly as it can out of the barrel, eliminating as much bullet yaw as possible.
Twisting the fastest rate possible due to the fact that one day you may wake up and decide what you really want drives you to shoot heavy for twist rate bullets, whether or not you want to go there or not.
For example, when I want to shoot 140g-150g cup and core bullets in my 7 mags and 7 sTW, I shoot an 11 twist and three grooves. This is going to drop pressure while boosting velocity. The same thing applies to 30-cal hunting bullets, you slow the RPMs down, and they penetrate better, so lighter bullets perform in some respects like heavier bullets.
All of the twist rate recommendations are steeped in Traditions, but when you start actually using a twist rate calculator, the learning curve is quite impressive. The Berger Bullet website can give you a glimpse into what is necessary on the twist rate for a particular bullet.
Very fast Bullet RPM makes bullet jackets open up faster(316,000+), we have seen this over and over again on varmint rigs. So, do you want your big game bullet to blow up quicker in an animal, then twist if faster? This may also introduce bullets blowing up prematurely, especially in barrels with cracking in the bore and rough finish due to heat/ pressure.
In the 6.5 caliber, the 147g and in the 7mm, the 180g eldms are famous for blowing up when twisted too fast or shot too hard. The Engraving pressure as the bullet enters the lands is tremendous with the pressure spike that accompanies it, and controlling bullet base deformation is critical.
Berger had one heck of a time with his first 6mm 105's when they came out due to boat tails deforming during obturation as pictures taken by Bill Davis at Aberdine Proving Grounds showed. They changed the alloy mix which cured the problem-Olympic Comp bullets.
In the 22 caliber, 6.5 twist is needed for hot weather with 90g Bergers, and throat accordingly, which means the use of lighter bullets you should consider a crap shoot.
Prudent to take a step back, Use a ballistics calculator, plug in your bullet, velocity, and temp, and see what gives you a 1.5 stabilization factor, with a 1.2 being marginal during certain weather and elevations. When shooting hot rod cartridges, I always use a slower-than-normal twist, I am looking for that magic RPM rate that I want given the velocity of the cartridge, elevation, temp, etc.
I do not shoot monos as a rule with the exception of 110g Barnes ttsx in my 270, 80g ttsx in a 257 Weatherby, and 80g TTSX in a 243 win.
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Given everything in the load is the same, I do not see how this is possible.
How much energy do you think bullet friction against the barrel uses?
kfreeze
Well-Known Member
Exactly the point I was making. If you only want to be able to run hammers, then spin them faster. And with hammers, the faster the better. I don't like limiting myself like that. If you don't limit yourself, you will be able see closer to benchrest groups out of your hunting rifle. 1/4 moa out of a custom hunting rifle seems to be the target for myself and the group of guys I shoot with.
I have PO Ackley manuals, he spoke of the speeds and this is what he focused on. He made rifles, lots of converted Mausers. He ran twist rates appropriate for the bullets intended. He had his own barrel-making machine.
Pac Nor runs a larger bore dia than other barrel makers for one thing, so you have less engraving pressures, sound familiar? Have you ever tried to fit a reamer pilot for one of the Pac Nor barrels, they seem huge!
A slower twist rate generates less pressure, or pressure is extended over a longer distance in the bore, so the burning chamber of a slow twist may be longer than it is in the faster twist rate. First time I saw this issue was with a 22 PPC comparing two identical barrels, cut with the same reamer. The 9 twist was much more sensitive to top-end pressures vs a 14 twist with identical bore dia, Hart SS barrels.
Every three-groove barrel I have ever had from Pac Nor, Lilja, and X caliber has been "fast" barrels, and I have never had one of these barrels that did not shoot tiny bug holes. X Caliber has a 3 Groove that is a 3R design, mine is in a 6 Dasher and it is a shooter.
I have not seen pressures change much on 2" twist rate change, but have on 4-5" twist rate changes in the same caliber, with the same brand of barrels cut with the same freebore amounts...key words "from the same barrel maker". Bore diameters from maker to maker do vary, which has an impact on pressure.
A friend is shooting a 6 Gibbs, shooting the 70g Nosler ballistic tips at 4400fps+, long 30" barrel, and slow twist, his deer rifle. His backup bullet is the 90g Nosler ballistic tips for the same slow twist. He has killed an incredible number of deer with the 55g Nosler ballistic tips in another rifle with the 6 Gibbs.
My point is, to twist your cartridge for the atmospherics, and throat geometry that you will be shooting/hunting, with bullets of weights and designs that you will be shooting. Great success is sure to follow with careful planning.
Somethings you have to try for yourself. In the 7 STW, 11 twist, Pac Nor Super Match with zero freebore, and the Pac nor 3 groove, 10T, zero freebore, 257 Weatherby, velocity and accuracy is beyond belief with speeds that no one would believe.
Pac Nor runs a larger bore dia than other barrel makers for one thing, so you have less engraving pressures, sound familiar? Have you ever tried to fit a reamer pilot for one of the Pac Nor barrels, they seem huge!
A slower twist rate generates less pressure, or pressure is extended over a longer distance in the bore, so the burning chamber of a slow twist may be longer than it is in the faster twist rate. First time I saw this issue was with a 22 PPC comparing two identical barrels, cut with the same reamer. The 9 twist was much more sensitive to top-end pressures vs a 14 twist with identical bore dia, Hart SS barrels.
Every three-groove barrel I have ever had from Pac Nor, Lilja, and X caliber has been "fast" barrels, and I have never had one of these barrels that did not shoot tiny bug holes. X Caliber has a 3 Groove that is a 3R design, mine is in a 6 Dasher and it is a shooter.
I have not seen pressures change much on 2" twist rate change, but have on 4-5" twist rate changes in the same caliber, with the same brand of barrels cut with the same freebore amounts...key words "from the same barrel maker". Bore diameters from maker to maker do vary, which has an impact on pressure.
A friend is shooting a 6 Gibbs, shooting the 70g Nosler ballistic tips at 4400fps+, long 30" barrel, and slow twist, his deer rifle. His backup bullet is the 90g Nosler ballistic tips for the same slow twist. He has killed an incredible number of deer with the 55g Nosler ballistic tips in another rifle with the 6 Gibbs.
My point is, to twist your cartridge for the atmospherics, and throat geometry that you will be shooting/hunting, with bullets of weights and designs that you will be shooting. Great success is sure to follow with careful planning.
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Never worked with any of those barrels with the exception of a Lilja on a old .308 I have. Only knowledge I have concerning lowering pressures are articles on moly bullets. It lowered pressure and velocity.
