Has anyone tried or heard of anyone playing with this cartridge?

[HARPERC]

It seems like the variables are 1) Bullet material/construction 2) The difference in twist high to low 3) How hard the bullet is initially driven.

The thought I keep coming back to is, I'd prefer any alteration to the bullet be done early in its travels down the bore.

The only reason I would likely use it is in something like an extreme 6.5. mono metal bullet where encountering that much resistance initially is kin to putting a penny on a railroad track. Maybe the fact one is considering such a thing, could be a sign we've gone to far.

Thanks Guys.

 

[gregsjt]

Check out this link: Frank from Snipershide just put a gain twist barrel on his Tikka .260, he talks about it quite a bit on his podcast, Everyday Sniper. You should check that out too, he does a better job at explaining it than I can. From what I gather, gain twist rifles could be a good solution for shooting heavy for caliber bullets, especially if you're going to be pushing the velocity limits. I think its actually easier on the bullets than forcing them into a tight twist right from the jump.

https://forum.snipershide.com/threads/gain-twist-in-depth-and-reloading.6886129/

 

[gregsjt]

 

[WildRose]

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.

That isn't even possible. As the twist tightens the original grooves have to continuously be re-cut to match the new twist.

 

[therifleman556]

That isn't even possible. As the twist tightens the original grooves have to continuously be re-cut to match the new twist.

I think this is a bit misleading. Although the angle of the grooves cut into the bullet will vary from tight twist to a lower twist barrel, the change a bullet sees in a gain twist barrel will be gradual enough to be almost unnoticeable.

It's difficult without seeing a bullet firsthand, but I picture the grooves in a bullet fired in a gain twist barrel to be either triangular or even hour-glass shaped.

 

[gregsjt]

That isn't even possible. As the twist tightens the original grooves have to continuously be re-cut to match the new twist.

Dude, this is going to be hard to explain in writing, I wish I had a white board!

Ok, imagine a five pointed star inside of a tube, each point of the star just touches the inside of the tube and the tube is 12" long. If you're looking staight from the end of the tube you see a star with a circle around it. Also imagine that the point that is pointing up is number 1.

Now I'm going to pull that five pointed star through the tube at a very consistent rate and I'm going to pull it through the tube the same rate every single time. So, the first time I pull the star through the tube I don't do anything to the tube while I'm pulling the star. When I get done all I have are 5 straight lines scratched on the inside of the tube, no twist.

Now, the second time I pull the star through the tube I'm going to twist the tube one full rotation around the star, if I time the twisting of the tube so that one full twist of the tube will end at precisely the same time that the star reaches the end of the tube I just created a 1:12" twist or in other words the number one point of the star will make one full rotation inside the tube in 12".

Now let's pretend that on the third time I'm going to vary the speed that I twist the tube while the star is being pulled through. So when I start I'm going to twist the tube at the same rate as the second time so by the time I hit 6" I've twisted the tube 1/2 of a roation. Then in the last six inches I twist the tube 1 full roation more. So instead of 1 full twist in 12" I made 1.5 rotations of the tube in the time it took for the star to be pulled through the tube.

I'v effectively just created a gain twist inside the tube, the first six inches is on pace for a 1 twist in 12" and the second half of the tube is a 1 twist in 6".

During that whole process the geometry of the star never changed! Meaning the lines inside the tube are spaced the same distance apart no matter how fast or slow I twisted the tube around the star.

I know this isn't exactly how they make the barrels but it's the easiest way I can think of to explain why the gain twist doesn't change the geometry of the lands and grooves. Hopefully it makes sense.

 

[gregsjt]

I think this is a bit misleading. Although the angle of the grooves cut into the bullet will vary from tight twist to a lower twist barrel, the change a bullet sees in a gain twist barrel will be gradual enough to be almost unnoticeable.

It's difficult without seeing a bullet firsthand, but I picture the grooves in a bullet fired in a gain twist barrel to be either triangular or even hour-glass shaped.

Ok, let's say you have two barrels, both barrels are 5 groove .30 cal. The first is a normal 1:10 twist and the second is a gain twist, say it starts at 1:12 and ends in 1:9. If you could recover a bullet fired from both barrels you wouldn't be able to tell which one was fired from which barrel by the rifling marks left on the bullet. They would both have 5 marks and each mark would be the same width.

 

[Edd]

The geometry does change with a change in twist. As twist increases the degree of angle increases.

 

[gregsjt]

This is true, but the distance between the lands and grooves or the shape of the lands and grooves does not.

 

[Edd]

The angle of land contact on the bullet changes. The groove in the bullet has to grow wider somewhere to accommodate this change.

 

[gregsjt]

I agree, but I think the bullet would have to be really long or the change in twist rate would have to be extreme to make that noticeable if you were looking at two recovered bullets.

 

[iowaelkbum]

The twist would have to change within the bearing surface of the bullet to have any "shearing effect" on the jacket.

 

[yobuck]

In answer to the OPs question, yes the 378 case has been necked down to 6.5.
Fact is it was done over 50 years ago by the late 6.5 guru Alex Hoyer of Lewistown PA, for a guy by name of Joe Reits of Sunbury PA. Hoyer died in 1970, and when the barrel shot out Reits took the gun to Howard Wolfe of Mifflinburg for a new barrel.
Wolfe refused, but apperently later did it with a modified shortened case he called the 30/378 Wolfe, known locally simply as the short version, or Wolfe version. Actually same case capacity as the modern 300 Norma.
Wolfe had developed a large 3 lug action for the full length version 30x378 in the 60s.

 

[Edd]

I agree, but I think the bullet would have to be really long or the change in twist rate would have to be extreme to make that noticeable if you were looking at two recovered bullets.

With a .500" long bearing surface, the difference between a 7" and 8" twist is about .007". The difference between a 7" and 12" twist is about .024".