Rechamber ?

legn4

Could a rifle in (bolt action) 338 Win Mag be rechambered to
340 Weatherby Mag ? From I see they are close , just asking.
Thanks

charliemeyer007

Overall length in the magazine box might be an issue. I would do a chamber cast to make sure everything cleans up with the new reamer. I didn't compare the actual dimensions.

https://en.wikipedia.org/wiki/.340_Weatherby_Magnum
https://en.wikipedia.org/wiki/.338_Winchester_Magnum

A buddy got a rifle from his dying mom. Bubba re-chambered a 7x61 S&H SaKo rifle to 7mm STW. Made a nice 2 shot rifle with proper ammo. The correct loads wouldn't fit in the mag box. Drop one in the chamber, place one in the mag, press it down - close bolt over top.

62fuelie

I just faced that question when I wanted to try building a long range rifle. I had a .338 Win Mag Weatherby Vanguard and did the calculations - It can be done, but I didn't think it was worth the difference in cost. I sent it to Douglas and they fitted a 26" 5A profile barrel and mounted a Gentry muzzle brake for about $200 more that the rechamber would have cost. I did have to spend $10 for a .300 Whby mag box to accommodate the long .340 round and use a .300 Whby mag follower as well, but now it functions very well. The only problem is, I tore the retina in my left eye(doing something else, not firing the .340) and now my doctor is limiting me to my .222 Rem for the moment. Probably wind up selling the .340.

In looking at the various candidate .338 caliber cartridges my research indicates that there is very little realistic difference in potential between the .340, the .338 RUM and the vaunted .338 Lapua. They are all capable of generating maximum velocities within 50-150 fps of each other depending on bullet weight for the 250-300 grain class of bullets. The Weatherby brass is expensive, until you start pricing Lapua brass. The Weatherby is the only round capable of being made from a variety of "donor" rounds from .300 H&H to the .375 H&H plus the .300 and .375 Whby's as well. The long bullets in this class all have driving surfaces in excess of .581" so the bullet is well engaged in the rifling before it fully leaves the case. This bridges the .314" free-bore of the Weatherby chamber and leaves the bullet aligned and stable.
FWIW

spirits

Cartridges like the 338 WM were conceived to work in standard length actions. If your bolt action is a standard length action in 338 WM, I don't believe the receiver length and the magazine box length would allow for the longer 340 WbyM cartridges.

tsr1965

It depends on what rifle, and what length action was used to build it. Most of them that chamber the standard short 7mm Rem, 300 Win, and 338 Winchester magnums, use the standard medium length 30-06 length action. If the rifle has the magnum length action, then I would not stop at the 340 Weatherby. Why burden yourself with pricey brass, and ammunition, with just a little bit more horsepower. I would chamber it to the 338 RUM. Better ammo and Brass availability, and getting to the class of the 338 Lapua performance.

nononsense

The .300 WBY case has the same dimensions as the .340 except for the neck diameter.





Pay attention to the discussions above which cover the magazine lengths of commercial actions. They are not all created equal.

Who is the barrel maker for the .338 WM? Some commercial barrels will not lend themselves to being re-chambered.

How many shots have been fired on this chamber and barrel? Too many rounds fired and the throat may too far advanced to allow for a quality re-chamber even if the new chamber is slightly longer. If there is substantial carbon build up in front of the throat on the original chamber, many gunsmiths will not run an expensive reamer into that barrel for fear of damaging the reamer.

I agree with the thinking that there are other cartridges to use instead of the expensive .340 Weatherby.

As above, I think the .338 RUM is a superb cartridge which has not been given the credit it deserves. One jump up from there is the .338 Edge which is the .300 RUM necked with some changes in the design of the throat and freebore, often noted as the .338 Edge Plus. These cartridges maintain the standard magnum rim diameter of 0.532" so you won't have to rework the bolt also.

If I was finding that the re-chamber and all of the attending costs were growing beyond what I thought was reasonable, I would switch to an action which utilizes the Lapua bolt face but shoot the .338 Norma Magnum cartridge. Of all the .338's I have in process, this is my choice for the best cartridge.

Best.

nononsense

62fuelie,

quote:In looking at the various candidate .338 caliber cartridges my research indicates that there is very little realistic difference in potential between the .340, the .338 RUM and the vaunted .338 Lapua.

This is because of the limitation imposed by barrel length and chamber designs most commonly used outside of match and longer range target shooting. Surprisingly, you didn't include the .338 Norma Mag which is overtaking the Lapua when it comes to both hunting and competition.

When the barrel length and chamber design is matched to the cartridge/bullet and powder combination, the real differences start to show up. But this is not a simple generic solution. It's aimed [}:)] at the folks who choose to maximize the performance of any cartridge, not your everyday hunter and casual target shooter. Slower powders, longer barrels, heavier or even lighter bullets will show some decided differences.

Best.

penguin

Not worth the effort. You will never see the difference in performance,

nononsense

penguin,

quote:Not worth the effort. You will never see the difference in performance,

When posters fall back on the final effect of 'dead is dead', you are correct. But using that same logic the examples can be changed and down graded to something along the lines of the .223 Rem. in states where it is allowed. Dead is dead right? This same argument is often applied by the massive number of supporters of the .270 Win. and the .30-06 Springfield, no other cartridge is ever needed except for one of these two cartridges. But then the entire industry would collapse because of the lack of commerce.

However, when we keep the comparison intact, you will find that through some reloading you can achieve an additional 200 FPS increase using the the .340 WBY Mag over the .338 Win. Mag. With that increase comes a 500 ft/lb. increase in energy on target. This is using the same length barrel and bullet, obviously using different powders since the .338 Win. Mag. has an 86 grain capacity while the .340 WBY has a 100 grain capacity.

Don't forget to take into account an individual's desire to try something different. Often when asked why a shooters chose a particular cartridge, the reply is 'just because I wanted to' and that is a perfectly good answer. There is no better justification.

Best.