Having seen lots of discussion on various forums, I asked the Weatherby custom shop about throat length (sometimes referred to as free bore) on their rifles. This built in "jump" allows the pressure spike to be somewhat mitigated. Non-Weatherby calibers do not have this throat length adjustment.

Cartridge Throat length (free bore)
.224 Weatherby Magnum .162
.240 Weatherby Magnum .169
.257 Weatherby Magnum .378
.270 Weatherby Magnum .378
7MM Weatherby Magnum .378
.300 Weatherby Magnum .361
.340 Weatherby Magnum .373
.375 Weatherby Magnum .373
.378 Weatherby Magnum .756
.416 Weatherby Magnum .239
.460 Weatherby Magnum .756
.30-378 Weatherby Magnum .361
.338-378 Weatherby Magnum .361

I just thought I would share what they told me.

All of which is why I never liked Weatherby cartridges, and have no use for the rifles either. No hate mail from Wby lovers, please.

Probably the reason why Schultz and Larsen also generously free bored their rifles for the 7x61 S&H Magnum, 308 Norma Magnum and 358 Norma Magnum cartridges, all top performing cartridges in their calibres and in the S&L rifle.

In 1956 Roy Weatherby stopped using Mauser actions and used Schultz and Larsen M54 actions for his 378WM cartridge before he came out with his own Mark V action a couple of years later. His Mark V used a few of the good features of the S&L rifle.

Interesting.
I currently have barrels in 270 Weatherby (.375" freebore), 300 Weatherby (.375" freebore), 340 Weatherby (.500" freebore) and 375 Weatherby (.500" freebore).
It appears recent changes have been made to certain cartridges, I knew the 270 and 300 had been reduced, they both were .500" originally, as to the 22 and 24, they never had freebore as such.
Didn't know the 378 had over .700" freebore, that's very interesting.

Thanks for those specs.

Cheers.

I have heard much to do over free boring, always without real facts or basis..It works, and those Wbys, though not my cup of tea, sure do shoot accurately and get the velocity..The down side of free boring is a waste of time..It hurts nothing...

I like a long throat and long magazine in most calibers, but its not free boring, as some contend, its simply a long throat and I seat the bullets way out so I can use more powder at the same pressure, and get additional velocity, if I shoot factory ammo in one of my guns so set up, then it is free boring and the bullets have to jump, and it has never effected accuracy or velocity. I cantend and have proven to myself that the jump to the lands has noting to do with anything other than if it does not work then you have a bad barrel and your blaming it on the jump...I will argue that until hell freezes over. Good barrels shoot, bad barrels don't shoot so good.

quote:

Originally posted by Atkinson:
I have heard much to do over free boring, always without real facts or basis..It works, and those Wbys, though not my cup of tea, sure do shoot accurately and get the velocity..The down side of free boring is a waste of time..It hurts nothing...

I like a long throat and long magazine in most calibers, but its not free boring, as some contend, its simply a long throat and I seat the bullets way out so I can use more powder at the same pressure, and get additional velocity, if I shoot factory ammo in one of my guns so set up, then it is free boring and the bullets have to jump, and it has never effected accuracy or velocity. I cantend and have proven to myself that the jump to the lands has noting to do with anything other than if it does not work then you have a bad barrel and your blaming it on the jump...I will argue that until hell freezes over. Good barrels shoot, bad barrels don't shoot so good.

Finally, somebody who thinks the same as me.
I have long throated nearly every barrel I have ever had chambered, the Weatherby's being freebored have never had any accuracy issues that I've ever seen, except in bad barrels, as you, quite rightly, point out.
All of my target barrels are throated to suit the bullet they shoot so that it doesn't protrude below the neck/shoulder juncture. This is how I was taught to do this, if I shoot factory ammo for fireforming, or just to get brass, the jump is long, but accuracy doesn't suffer.

Cheers.

I had a NULA .257 Wby Mag which restricts box length so I had mine throated at .187" and had no pressure issues.

Thanks for the data.

I once tried to find out how much freebore my 460 had by seating a bullet out as far as I could in a partially neck-sized case but I never hit the rifling.

There are couple of things about Wby freebore and freebore in general that most shooters are not aware of.

Firstly, with Wby the secion from case mouth to rifling is parallel or a cylinder as opposed to tapering down. For a Wby to be on spec the freebore section is .0005 over bullet diameter. A Wby chambering where the diameter of the freebore is too large will cause you to pull your hair out.

Secondly with non Wby calibres like 270 Win or 300 Win for example when you change seating depth a little and get a gain in accuracy the reason is a change in ignition characteristics not the amount of bullet jump.

The two calibres, that is Wby and non Wby, that I have tried over the years are the 300 Win and 300 Wby. Rilfes have included switch barrel bench style rifles.

So a couple of generalities.

The 300 Win will deliver the best accuracy and simply because you have more ability to "tune" the ignition. However, we are talking about very accurate rifles for this to become apparent.

Because you can tune the ignition of the 300 Win you will be able to get high levels of accuracy across a wider range of powders, projectiles and primers.

However, there a couple of pluses come with the Wby chambering style.

Firstly (assuming all else is equal) the Wby is more likely to put the first shot from a clean barrel or a barrel with cold hard fouling, into the group.

Secondly, the Wby will do more of its potential velocity with powders that would normally considered a bit fast. For example, a 300 Wby will do much better with Varget/4064 than will a 300 Win.

Thirdly, pressure spikes are not the same issue whether those spikes are caused by barrel fouling conditions or a very hot day.

In summary, for an sporting weight rifle I would prefer a Wby style chambering, assuming of course that the freebore diameter is on spec, than a non Wby chambering.

However, for an extreme accuracy gun then I would choose a non Wby chambering. In other words I would choose a 300 Win or 300 RUM over a 300 Wby.

One last point which hardly anyone here will be interested in but in the interests of completing the differences, Wby chamberings are not as good for very reduced loads as ignition can be the problem. This is very evident with both the 378 and 460.

If you can seat a bullet where it sits on the lands you will be amazed at low you can drop loads and using normal rifle powders and with outstanding accuracy. The Wby chambering does not allow that or at least not to the same extent.