From the FAQ at www.weatherby.com

The freebore lengths refer to the parallel-sided portion of the throat, and do not include the leade that tapers into full rifling engagement.
This parallel-sided freebore itself is usally pretty tight.
Example: Both the .375 Wby and the .378 WBY have freebore diameters of .3756" to allow free jump of .3750" bullets.
0.0006" greater than bullet diameter.

The .378 WBY throat is way long, however, and so was the .375 WBY back in 1947.
Not so since 2001 rebirth of the formerly obsolete .375 WBY with new throat.

According to Weatherby:
.375 WBY: .373"
378 WBY: .756", more than twice as long as the former.

IMHO, the .375 WBY is the most perfectly throated of the lot, just sayin'.

Wow. Looks like you can see what people were thinking thru the years. 416 looks totally normal and the 375 is pretty close. I had no idea the 460 had a flying leap to the rifling.

The fact I'm a moron will be apparent in the question I'm about to ask...sorry...

What do we do with feeebore? In other words, Weatherby printed this information on freebore because there was a need to know it. Does this simply give the handloader more information to find the seating depth of his rounds? What would the 'ah ha!' be when looking at this chart? And why is the 375 perfect, because the freebore is closest to the bullet diameter?

See, lots of stupid questions, but I have a few more brain sulci that need filling up...

quote:

Originally posted by BaxterB:
The fact I'm a moron will be apparent in the question I'm about to ask...sorry...

What do we do with feeebore? In other words, Weatherby printed this information on freebore because there was a need to know it. Does this simply give the handloader more information to find the seating depth of his rounds? What would the 'ah ha!' be when looking at this chart? And why is the 375 perfect, because the freebore is closest to the bullet diameter?

See, lots of stupid questions, but I have a few more brain sulci that need filling up...

BaxterB,

I am just yanking your chain.
However:
A throat should not be too wide and long, sloppy, as to allow the bullet to wobble too much before becoming fully engaged in rifling,
lest accuracy suffer.

Here is a sample of what the modernized .375 WbyMag throat can do with the accurate bullet:



This bullet was a Bridger Bullets copy of the Walterhog .375-caliber/300-grain bullet.

A bit of freebore is not a bad thing for accuracy, and it can make for top velocity at modest pressure.

I was aiming at the spot where the "POA" X is located.
I was planning to get as many 3-shot groups as possible on one piece of paper at 100-yard range.
I was pleasantly shocked.

Very good, RIP, thanks for the extra info. This whole 375 Wby thing (or more complexly the 375/404) are interesting for a bucolic hick such as myself... ;-)

I've read that one of the wildcat methods in the past was to freebore a rifle to 2 and even 3 calibre lengths, while 'maintaining inherent accuracy'. For a .458 (=460Weatherby) that would be .916" to 1.374", which is a lot of freebore.

Does anyone have experience with such freebores in big bores? For example, with a 1 inch freebore, or averaging the 2x-3x as 2.5x, say a .500" with 1.25" freebore?


Just how fast can a bullet be going and the riflings can still have the strength to impart twist? I've also read that some tank shells only pick up their twist toward the end of their barrel, which seems counterintuitive to me.

What kind of life expectancy does rifling have if it has to initiate twist after a bullet has been launched and running for an inch?

Whether the bullet jumps 1/4" or 1", no significant difference on rifling stress, my guess.
Bullet is still starting off, and accelerating, much more slowly than the gas from the powder burn.
Gas blow by in the freebore before the bullet seals the rifling?
That happens to some degree with any throat.
More so with longer free bore.
Keeping the freebore just 0.0006" over the bullet diameter, ought to keep the gas cutting minimized, however long the freebore.

I have compared a 1947-vintage-throated .375 WBY (~3/4"-long freebore of ??? diameter) to a 2001-throated .375 WBY (~3/8"-long freebore of +0.0006" diameter):
The old throat gave horrible accuracy and -100 fps velocity with the same ammo that did supremely well in the new throat.
Both rifles were made for me, from new barrels,
neither was "worn out."

Some freebore good. Too much freebore bad.

I can only hope the few Weatherby rifles still having freebores longer than bullet diameter are tightened up to only +.0006" over bullet diameter,
in the parallel-sided freebore diameter.


Gain twist rifling? Starts slow and speeds up toward the muzzle?
That has certainly not dominated the sporting rifle.

Tanks: Smooth bore with sabot and fin-stabilized/dart-stabilized flechette/rod-like penetrators of depleted uranium.
I wonder if they ever wear out those barrels?

quote:

I have compared a 1947-vintage-throated .375 WBY (~3/4"-long freebore of ??? diameter) to a 2001-throated .375 WBY (~3/8"-long freebore of +0.0006" diameter):
The old throat gave horrible accuracy and -100 fps velocity with the same ammo that did supremely well in the new throat.
Both rifles were made for me, from new barrels,
neither was "worn out."

Some freebore good. Too much freebore bad.

that's the colloquial wisdom.

quote:

Originally posted by 416Tanzan:
I've read that one of the wildcat methods in the past was to freebore a rifle to 2 and even 3 calibre lengths, while 'maintaining inherent accuracy'. For a .458 (=460Weatherby) that would be .916" to 1.374", which is a lot of freebore.

Does anyone have experience with such freebores in big bores? For example, with a 1 inch freebore, or averaging the 2x-3x as 2.5x, say a .500" with 1.25" freebore?


Just how fast can a bullet be going and the riflings can still have the strength to impart twist? I've also read that some tank shells only pick up their twist toward the end of their barrel, which seems counterintuitive to me.

What kind of life expectancy does rifling have if it has to initiate twist after a bullet has been launched and running for an inch?

I think that the first wildcat cartridges were designed for only one purpose, a maximum velocity.

The freebore was used as an enlarged chamber where more volume, more powder = more velocity.


I've first hand experience with .460Wea and standard .750" factory freebores and also my own fuck up 1" freebore to shoot 730gr. casts.

The difference is zero in all counts. I think that after several thousands of rounds I should been able to tell the difference, but I can't.

Pyzda

I've tried various Freebore combos and basically as I've said before have found very little effect. At long range excessive freeborn will reduce accuracy, but not that drastically either . The .460 why despite its excessive freeborn still Expands the belt .005 with new brass in any attempt to exceed 2600fps with a 500gr bullet. I was NEVER and I repeat NEVER able to attain 2700fps without some really uncomfortable extractor GOUGES and belt expansion. -Rob

quote:

Originally posted by Robgunbuilder:
I've tried various Freebore combos and basically as I've said before have found very little effect. At long range excessive freeborn will reduce accuracy, but not that drastically either . The .460 why despite its excessive freeborn still Expands the belt .005 with new brass in any attempt to exceed 2600fps with a 500gr bullet. I was NEVER and I repeat NEVER able to attain 2700fps without some really uncomfortable extractor GOUGES and belt expansion. -Rob

Agree. I Graduated from .458 WinMag to 460 WBY in 1985, and if you ever got to 2700 fps with a factory Wby Mark V, you might have a pierced primer and some smoke in your face.

As Pyzda points out, free-bore is good for extra velocity, via extra case capacity through extra COL. Limited by box length for COL.
And limited by accuracy effects, which are minor as long as the throat is not too sloppy,
as Rob said.

Maybe a +4.000" COL and box length would allow the 460Wby to get a 500-grain Hornady up to 2700 fps, at usual max pressure. It would not hurt accuracy.
I never tried it.

Hornady 500gr./2700fps safely from a factory .460Wea with the integral muzzle brake is virtually impossible. In 81 where my .460Wea was my first and only rifle I ruined 220 cases (expanded primer pockets) on the very first reload (125gr/500gr Hornadys crimped). Those days I didn't have a chronograph to measure the velocity. When this load was chronographed (this time as an experiment only) and fired from a tyre several months later it did 2695fps.

I've dropped the powder charge to 122gr. and I got myself a chronograph. With this reduction of powder the same factory muzzle brake equiped barrel vas getting honest 2620fps. With this load the Norma brass lasts about 4-5 reloads. The same load in the 27" barrel without a muzzle brake did 2680-2710fps. depending on the heat of the day.

The same 122gr./500gr load did 2540-2560fps. in several 22" barrels without a muzzle brake.

I think that the .460Wea as good as it is the first published factory loads were just one of data. Im my opinion it is not a true 8000fp. but rather 7000-7500fp. cartridge at the best of the time.

Pyzda

quote:

I think that the .460Wea as good as it is the first published factory loads were just one of data. Im my opinion it is not a true 8000fp. but rather 7000-7500fp. cartridge at the best of the time.

That estimate fits much better with other estimates. I would put the 500Mbogo/500A2 and also the 500 Jeffrey at 8000+, which makes sense since they are either wider calibres of the same basic case, or a larger case+calibre. Without knowledge or testing, I feel that the 505 Gibbs ought to be good for 9000ftlbs. Since I am happy to be limited to 7000 ftlbs., that makes me a happy camper with a 500AccRel (Nyati, short freebore).

Interesting. I knew my own .460 was more than .5", I just didn't know how much. And with that much freebore, I would think accuracy would suffer. Although I've never shot anything close to 1.5 m.o.a., the target that came with my rifle shows less than that.

And, fwiw, my 24" rifle shoots 500 gr. factory solids at around 2550 fps/7220 fp of energy.

Joe

your barrel seems to be a slow barrel, as I would think 2600fps with a factory ammo would be the expected norm.

1.5 MOA accuracy also shouldn't be out of question, but rather expected more or less.

However in case of the .460Wea cartridge never try to blame the .750" freebore for the luck of accuracy.

Do your part and you will get less than a MOA with several different loads.

Pyzda

120 Gr of 4350 with a 500Gr hornady gives me 2625. No pressure signs what so ever. I dont use a muzzle break.

quote:

Tanks: Smooth bore with sabot and fin-stabilized/dart-stabilized flechette/rod-like penetrators of depleted uranium.
I wonder if they ever wear out those barrels?

RIP

Use to be 400-500 rds but I think they up graded ammo specs so am not sure what it is now.

edit-

Rheinmetall's L/44 tank gun has a caliber of 120 mm, and a length of 44 calibers (5.28 meters (17.3 ft)).[23] The gun's barrel weighs 1,190 kilograms (2,600 lb),[24] and on the M1 Abrams the gun mount weighs 3,317 kilograms (7,310 lb),[25] while the new barrel (L/55) is 55 calibers long, 1.30 meters (4.3 ft) longer. The bore evacuator and the gun's thermal sleeve, designed to regulate the temperature of the barrel, are made of glass-reinforced plastic, while the barrel has a chrome lining to increase barrel life.[5] Originally the gun had a barrel life of between 400 and 500 rounds, but with recent advances in propellant technology the average life decreased to 260 rounds. In some cases, barrels have had to be replaced after firing only 50 projectiles.[26] The gun's recoil mechanism is composed of two hydraulic retarders and a hydropneumatic assembly.[5]


did some quick GOOGLE yep they changed specs

Cross L,
Tanks for that.
I googled it up too and found the quote,
but did not find the MOT accuracy specified nor what the latest propellant is.
But surely hitting another tank beyond the horizon is more than adequate minute-of-tank,
and it ain't blackpowder.