Weatherby Free Bore?

[elkaholic]

Same here, this is why I never draw a conclusion about a load anymore till I shoot it at 300 yards.

Jeff

+ 3 on that one! Especially true with some of the longer vld bullets. Sometimes takes them a bit to stabilize.....Rich

 

[wildcat westerner]

Free bore is what made Weatherby so much money, not accuracy. The company could advertise a certain cartridge at a high velocity back then which was much higher than its competition. The higher velocity was gained by higher pressure loadings for its catridges and the "jump" or freebore, before the bullet entered the lands of the rifle barrel. People wanting accuracy for these cartridges had them chambered with no freebore in custom barrels, with no concern for velocity since there was ample case volume for loading this cartridge to a higher velocity in the first place. I knew a shooter in Montana who had his Winchester chambered in .300 Weatherby with a slightly heavier barrel and no freebore. That man could shoot! He was one of the few magnum shooters at that time who could precisely place a projectile on target at long range. My view opf the .300 Weatherby cartridge changed solely due to his long range skills, long before rangefinders, better recoil pads, muzzlebrakes, and huge case capacity cartridges.

Happy New Year,

Gene So

 

[NorthernWeatherby]

Well this might be a little off topic, but what if you swapped to a gain twist barrel, and reduced free bore, would you be able to duplicate the pressure/velocity? What effect, if any, would it have on accuracy??

 

[Bart B]

Well this might be a little off topic, but what if you swapped to a gain twist barrel, and reduced free bore, would you be able to duplicate the pressure/velocity? What effect, if any, would it have on accuracy??

Nobody makes a gain twist rifling uniform enough to have the pitch curve's change rate uniformly engrave the bullet. Accuracy will suffer. Gain twists went out with the dish water when jacketed bullets became "the" bullet for best accuracy over a hundred years ago.

Most makers of barrels used to shoot most accurate all agree that the biggest single reason for a barrel with zero tolerance bore and groove dimensions not shooting accurate is the twist rate ain't uniform. There's a few places that measure twist uniforming. And some folks cry in their milk when they learn their otherwise perfect barrel has irregular twist rate changes a few places in the bore.

Bullets typically glide easily into rifling whose helix angle is only about 5 to 6 degrees; not enough to cause the bullet to jump the rifling at even the highest initial velocites out of the case that's only a few hundred feet per second. Some folks feel a gain twist starting out with a slower than what's best for the bullet in flight will allow higher initial velocities and therefore higher muzzle velocities can be done with great accuracy. This is number 24 on the list of accurate shooting myths.

 

[elkaholic]

Well this might be a little off topic, but what if you swapped to a gain twist barrel, and reduced free bore, would you be able to duplicate the pressure/velocity? What effect, if any, would it have on accuracy??

I talked at length with the Bartlein barrel folks and they told me that gain twist "does not" increase velocity, at least in any significant amount. They also stated that the jury is still out on more or less accurate. I have heard that if the rifling is perfect all the way to the muzzle, the accuracy can not be improved by gain twist. Having said that, a slight gain can stabilize the bullet at the muzzle in a less than perfect barrel. I do know that there is at least one 100 yd. benchrester that is setting some records with a gainer. I just ordered on for my 300 Sherman from Bartlein.....Rich

 

[wildcat westerner]

Sounds like everybody has a part of the puzzle here. Ultimately chamber pressure should equate to velocity, assuming cases of the same capacity. If that bullet starts moving against less resistance ( as in a freebore situation) chamber pressure has to be lessened. Even if we are talking milliseconds here, the only reason why a rifle doesn't blow up every single time you fire it is that the bullet exists the barrel and the gas expansion is no longer contained. Obviously the bullets' resistance as it passes down the barrel is a factor in pressure. Freebore allows the bullet in a barrel to pass through that barrel quicker. Therefore, less time in the barrel due to less resistance ( of the freebore)and thus lower pressure.

Gene so

 

[NorthernWeatherby]

Well that about settles it, I will be spending my afternoon researching gain twist, and free bore. I am a little sceptical that the gain twist is out the window as far as concepts, seing as how it is still used in custom barrels in places. But that is a topic for another thread........On free bore mine causes me no issues to as far as I shoot app 700yds, but we will see shen I go further.gun)

 

[linksmechanic]

Nobody makes a gain twist rifling uniform enough to have the pitch curve's change rate uniformly engrave the bullet. Accuracy will suffer. Gain twists went out with the dish water when jacketed bullets became "the" bullet for best accuracy over a hundred years ago.

Most makers of barrels used to shoot most accurate all agree that the biggest single reason for a barrel with zero tolerance bore and groove dimensions not shooting accurate is the twist rate ain't uniform. There's a few places that measure twist uniforming. And some folks cry in their milk when they learn their otherwise perfect barrel has irregular twist rate changes a few places in the bore.

Bullets typically glide easily into rifling whose helix angle is only about 5 to 6 degrees; not enough to cause the bullet to jump the rifling at even the highest initial velocites out of the case that's only a few hundred feet per second. Some folks feel a gain twist starting out with a slower than what's best for the bullet in flight will allow higher initial velocities and therefore higher muzzle velocities can be done with great accuracy. This is number 24 on the list of accurate shooting myths.

S&W Has gain twist rifling in their 460 magnum "X" Frame revolver and it is the most accurate revolver I have ever shot.

 

[Hired Gun]

I was waiting for someone to point out the 460S&W. I know the pistol is accurate but still have no factual opinion on gain twist. To think aloud for a secound though it sounds like a good idea to gently accellerate the twist of the bullet then to actually do that the rifling twist rate must change and thereby the initial engraving on the bullet will no longer match the beginning riflings and will exit the barrell much liker a cross threaded bolt. (slightly galled)

Best group ever out of my 300Wby Accumark is 3" and 885 yards for 3 shots. Many sub 1/2 MOA groups with Accubonds. When the weather lets up I have a batch of 210 Bergers I have high expectations for.


I'm not a balistic engineer but I did wear my Long Range Hunting.com T-Shirt today!