I was wondering if any one has tried to neck up a .300 or .375 RUM to a .408 to shoot woodleighs match bullets or similar. Sort of a poor mans slower cheytac? I want to try it on a rem 700 ultramag action But need to see how many fatal flaws are in my master plan or if it would be a good 1500-2000 yd caliber.

That sounds like an interesting cartridge.
For what it's worth. I've toyed with the idea on a 416 Weatherby case. It should be easliy adapted to the CZ 550 magnum action or just use the Mark V. If you look at the performance of the 416 Weatherby, which would give you a slight capacity edge, It would give you an idea of what velocity you might achieve.

Dimensions on the Weatherby case necked to .408 with a .306 (75% of bullet diameter) neck length and 40 degree shoulder and .009 body taper, water capacity would be about 139 grains.
Lehigh has a 400gn match VLD style bullet, which appears to have a nose to crimp length of 1.2". This would give you an OAL of 4.113. A bit too long for magazines. Twist rates would need to be faster than 1 in 14" as the estimated velocity would be between 2500 and 2600 fps. But that is pruely and estimate since nothing has been committed to steel and is pruely academic.

At 2600 fps and a 300 yard zero you would need about 23-24 minutes of elevation for 1000 yards. Impact velocities at 1K would be 1700+ with energies of over 2500 fpe.

Your 408x375UM would probably give up between 100 and 200 fps initial velocity. I'd have to pencil it out, but that is just a quick guess.

I've already done a 408 but as a hunting round. Designed as a standard length bolt action 40 cal rifle with recoil of the 375 H&H. As it turned out, it can easily duplicate the 450-400NE but with better versatility. I can shoot all the 41 mag pistol bullets and the cast bullets for the 40-65 (et al) as practice fodder. Premium bullets loaded provocatively can be back ups in the magazine. As it turns out it makes a nice big brother to the 358 Norma.

good luck with your project

Todd

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"Never ask a question you don't want answered" LOL

Sounds very cool and expensive.

Remington doesn't make Ultra action that just use different magazine and follower. I could be wrong but the inside on a long action magazine is 3.725" appr. so that handle the OAL @ 3.600" Wyatt makes extended for the Ultra that let you seat out to 3.825" but need a gunsmith to put that in at least I did.

Depending on how long those bullets are you may loose case capacity you sure want to invest in some cases and bullets see usable case capacity is.

I sure can understand want to do it on beltless mag case and if you did it on the Wby your on a belted case. the 408 cheytac has a H20 of 185gr and the 140gr H20 for the 416 Wby as kaytod mentioned and 110gr H20 for the RUM case.

Not sure if they have a lock on the Cheytac reamer but in the long run might be better to buy a reamer and cases and lot depends how much less of the 408 Cheytac your willing to settle for. those guys were pretty smart pick the 505 Gibbs case.

you can do a search their some other wildcats for the 408 and I think you can get them off sniper-hide. Well good luck

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This thread got my curiosity up. So, I called Hornady and they figured my 10.6mm Wildcat would only spin their 450 gr. match bullet 115KRPM. They think 185-200+KRPM is what the doctor ordered. So, in my rifle, a 1 in 11 twist would be about right. I'd like to try these anyway, but if they keyhole, that partial box would make an expensive paper weight. Years ago, Speer made a very long 400 gr. .416 Spitzer, with a flat base. I don't know which round it was made for, though. My 1 in 14 twist was supposed to do it all, but maybe not with this match bullet made for the Barretts.

Thanks for all of the info guys. I know there is not really an ultra action but after reading these post it would seem that I need to look at a larger case but I think the ones that will be sufficient are all going to be belted. Also I think I will need a lapua length surgeon or something of the like. It's unfortunate that we don't have a suplus of rigby rifles like our friends across the big water. The two cases I'm looking at now are the .338 lapua with improved shoulder and the .338 Norma. I think going to these cases would be stepping over dollars to pick up dimes but on the other foot cheytac brass is more than scarce apparently. But if all you fellows that are smarter than I am say this is dead in the water then I will probably just order the cheytac reamer and be done if its not proprietary.

After thought sorry. I think I read that the belt on a Weatherby is cosmetic because of the double radius shoulder but I'm probably wrong(been "THAT" kind of day) thanks.