re: Solutions to non-problems
I've read this discussion with great interest, and it got me intersted in doing a little research in the ol' sportin' library.
First off, the case head diminsion of the .240 Weahterby is 0.4720, while the case head of a .30-'06 and derrivatives is 0.4730, and the case heads of .308 Winchester and .243 Winchester are a little smaller, at 0.4570. On a Model 98 Mauser action or clone, like an Interarms Mark X, I wouldn't think the difference would be enough to merit changing the bolt face to accomodate a conversion and the extractor ought to snap right into the extraction groove of the .240 Weatherby case just fine.
The action length issue has already been addressed. If you've got a rifle with a standard ".30-'06" length action, then it will accomidate the .240 Weatherby, length-wise.
The "Knox Form" -that is the larger diameter of a barrel around the chamber- might indeed be an issue.
But pressure-wise, Norma, who loads Weatherby's proprietary rounds, lists maximum working pressure for the .240 WM at 55,100 PSI (according to the Speer Manual) while the .243 Win tops out at 52,000 C.U.P. -probably not enough difference there to get exited about, given that one is in PSI and the other is in copper units, and not that far apart when you convert one unit of measure to the other.
In my view, the question as to whether or not conversion from a .243 built on a standard length action to a .240 WM which also takes a standard length action isn't one of whether or not such a conversion can be done but a question of why would anyone want to do it.
There is a reason why the .240 WM never exactly set the shooting world on fire in terms of acceptence. In many ways, it's a solution to a non-problem.
It is waaaay over bore capacity in terms of the size of it's combustion chamber. As a result, the expansion ratio isn't that great and is far from being as effecient as a .243 Winchester is. In theory, the .243, being short and squat, should be more accurate than the .240 WM because of it's higher expansion ratio, greater effeciency, and more consistant igniton that comes with the shorter powder column. With a 6mm on big game, it would seem to me that shot placement is even more critical than it would be with a larger caliber, so I'd rather have accuracy over the additional velocity. In this case, I'd most definitely rather have it because most 6mm component bullets are designed for cartirdges in the .243 / 6mm Remington class and are intended to perform best at the velocites that those cartridges generate.
Then, with the .240 Weatherby, you also get that silly belted case, but I digress... In this case, on this round, the belt is strictly cosmetic, offering no real advantage while offering all of the disadvanteges of belted cases simultaneously.
And you're still stuck with 6mm bullets,which lack mass and sectional density at the same time.
It's amazing what happens, though, when you take that same size of combustion chamber and open it up to take .277, .284, or .308 bullets. Do that, and you get the ability to deliver bullets that have the mass and sectional desnity to get the job done when hunting non-dangerous game.
You basically get a .270 Winchester, .280 Remington, or a .30-'06.
Taste is relative. Before I went off trying to drive 6mm bullets with a .30-'06 combustion chamber, or something very close to it in the form of the .240 Weatherby, I'd try one of the less daring alternatives first.
Who am I kidding? I actually wouldn't do any of that. I'd stick with my .30-'06. By doing that, I never have to ask if my cartridge shoots flat enough to hit game at ranges that I am comfortable shooting it at. I never have to worry about whether or not I have enough downrange energy to cleanly harvest the animals that I pusrue. I never have to worry about whether I have enough penetration to reach the vitals if my shot angle relative to the target is less than ideal. I don't have to worry about obtaining loaded ammunition or compnents for reloading.
Boring? Yes. But effective? Most definitely. In my view, the old .30-'06 is still the greatest thing going in big game hunting rounds. It's still the standard by which everything else is judged. Some rounds might shoot flatter and offer less recoil, some might use a shorter, more effecient case and offer a tad more accuracy, and some might offer more power, but the '06 to me is still the perfect blend of trajectory, accuracy, managable recoil, and stellar downrange thump, all rolled into one commonly available package.
That's why doing things like trying to drive 6mm bullets with a .30-'06 combustion chamber doesn't make as much sense to me as just shooting a .30-'06 to begin with does.
Others, or course, are free to do whatever it is that they feel will best trip their trigger.