jasent
Well-Known Member
Barrels are like tires, you go through them faster on a hot rod
Has anyone tried or heard of anyone playing with this cartridge?
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WildRose
Well-Known Member
A gain twist in something this fast would shred bullets and probably lead to very dangerous pressures.
WildRose
Well-Known Member
I'm with the others, the 6.5x300wby is probably as far overbore as you want to go.
With the 6.5x378wby you're probably looking at 300-400rds max on barrel life.
There's a point of diminishing returns with respect to case size and bore diameter and you're way past the point of anything sensible putting that much powder behind a 6.5.
I had some friends wildcatting back in the 80's and 90's using Weatherby cases and 6.5 and 7mm bullets and they found universally with both that they were reaching the max of practicality with the .300 case.
HARPERC
Well-Known Member
Interesting-never had a gain twist. I did look into them lightly when last ordering a barrel. It seemed in my reading and conversations with barrel makers, the intent was to aid a bullet in surviving this transition, and reduction of initial pressures. Ultimately decided on a non-gain twist just to avoid a variable.
Curious to hear more of your thoughts on the subject.
Curious to hear more of your thoughts on the subject.
WildRose
Well-Known Member
Harper I looked into them a great deal when they first came out and found particularly that with high velocity rounds they were frequently tearing bullets apart.
Think of it this way. When the bullet hits the lans and grooves it is locked into them scoring the jacket. As the twist tightens tremendous forces work on the jacket as the grooves cut into the jacket go from being relatively straight to a tighter and tighter spiral.
If I were ever going to try one I think would have to shoot exclusively mono's through it to be safe.
HARPERC
Well-Known Member
......Which is what we're looking at. Everything has a structural limit, there are examples in the extreme cartridges that exceed copper jacket, and lead cores limits.
......Finding the limits for mono's will have it's own issues to work through.
......Fun though!
Thanks,
There is a way to "smooth" out the transition of bullet from case neck to bore ..... gradual engraving of bullet with rifling reduces early pressures/spikes leading to intact bullet and higher velocity as it exits the muzzle, accuracy is enhanced as well due to lessened sudden rotational impact stresses on the bullet, that ..... along with properly coated bullets can make all the difference,
of course that throat design has to be incorporated into the chamber reamer, I have been testing that design the last few months with Norma brass and recently with Petersen brass, it works .... barrel is a Rock Creek 30" 5R 1:7 twist,
The 6.5/378 Wby would certainly have more case capacity but you won't be able to use it due to the lack of super slow powders, in my scenario I'm limited to two powders that work, one of them is very temp sensitive and the other is hard to obtain, the other weak link I found was the Norma brass suffered from "premature exhaustion" with just a few pokes, the new 300 NM Peterson brass solved that softy issue and rides hard and long
of course that throat design has to be incorporated into the chamber reamer, I have been testing that design the last few months with Norma brass and recently with Petersen brass, it works .... barrel is a Rock Creek 30" 5R 1:7 twist,
The 6.5/378 Wby would certainly have more case capacity but you won't be able to use it due to the lack of super slow powders, in my scenario I'm limited to two powders that work, one of them is very temp sensitive and the other is hard to obtain, the other weak link I found was the Norma brass suffered from "premature exhaustion" with just a few pokes, the new 300 NM Peterson brass solved that softy issue and rides hard and long
I think a gain twist would do exactly the opposite.
WildRose
Well-Known Member
WildRose
Well-Known Member
Find yourself a fired bullet with clear grooves cut into from the lans and grooves of a barrel.
Imagine then twisting all of those grooves even tighter and all of the shearing stress on the jacket caused by same as they widen out.
With a traditional twist those forces don't magnify because from the moment it is engaged in the lands, nothing changes until it leaves the barrel.
With a gain twist as the bullet travels down the barrel the twist gets tighter and tighter with the lands constantly twisting and shearing the jacket in an attempt to cut new grooves to match the ever changing twist.
It would take someone with a whole lot more of a math and engineering brain than mine to explain it but it's like putting a wrench on the bullet and twisting it against the lands all the way down the barrel instead of it simply traveling the length of the barrel in the same grooves marked on the bullet at the point of engagement.
Imagine then twisting all of those grooves even tighter and all of the shearing stress on the jacket caused by same as they widen out.
With a traditional twist those forces don't magnify because from the moment it is engaged in the lands, nothing changes until it leaves the barrel.
With a gain twist as the bullet travels down the barrel the twist gets tighter and tighter with the lands constantly twisting and shearing the jacket in an attempt to cut new grooves to match the ever changing twist.
It would take someone with a whole lot more of a math and engineering brain than mine to explain it but it's like putting a wrench on the bullet and twisting it against the lands all the way down the barrel instead of it simply traveling the length of the barrel in the same grooves marked on the bullet at the point of engagement.
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HARPERC
Well-Known Member
I have seen both sides discussed and advocated. Which is more correct I don't know. Which factors make it more, or less feasible I can't say.
I did look seriously at it, and decided it's known to be an unknown. For that reason I decided against it for the initial effort. For essentially the same purpose stated by the OP. A heavy, 6.5 mono-metal, driven hard from a large case.
We're looking at a 160ish grain 6.5, that will need a 1-6" twist to stabilize.
As far as I can tell the purpose is to reduce those initial engraving issues. In my mind I can't visualize trading the initial stresses, for stress the length of the barrel, being a good thing. Bartlein refers to this as the bullet never going to "sleep".
There are shooters saying it works, and some military applications I'm told. Maybe it works in certain situations, but not in others.
For myself I'm curious enough that at some point I could try it, just for a learning experience if nothing else.
I did look seriously at it, and decided it's known to be an unknown. For that reason I decided against it for the initial effort. For essentially the same purpose stated by the OP. A heavy, 6.5 mono-metal, driven hard from a large case.
We're looking at a 160ish grain 6.5, that will need a 1-6" twist to stabilize.
As far as I can tell the purpose is to reduce those initial engraving issues. In my mind I can't visualize trading the initial stresses, for stress the length of the barrel, being a good thing. Bartlein refers to this as the bullet never going to "sleep".
There are shooters saying it works, and some military applications I'm told. Maybe it works in certain situations, but not in others.
For myself I'm curious enough that at some point I could try it, just for a learning experience if nothing else.
It would be similar to tapping a hole with fine threads and attempting to run a coarse thread screw into it, will run in a certain distance until you get cross threaded and things tighten up quick, creating a lot of torque and extreme pressure
WildRose
Well-Known Member
From the studying I did on the subject the big problem is going from a very slow twist like a 1:14- a very fast twist like a 1:7.
I'm not sure you'd see enough of a difference going from say a 1:10-1:7 but essentially as the twist gets faster widening out the grooves in the bullet there's a tremendous amount of shearing force on the jackets.
Still being addicted to speed myself the incredibly high velocities you can achieve with the gain twist barrels really appealed to me but the negatives just convinced me to stay with conventionally twisted barrels.
The geometry of the bore doesn't change as the twist is increased. The distance between the lands and grooves remains consistent from breech to muzzle. The grooves that are cut into the bullet at the start of the rifling are the exact same as at the muzzle, the whole thing just twists faster. Plus the twist from the start to the end should be a lot less like 1:8.5 to 1:7.5 for a 6.5 caliber or something similar.
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