Home Forums Hunting & Shooting Gunsmithing Winchester Model 70 suitable for RUMs?

I have a Winchester Model 70 Classic Stainless that was originally chambered from the factory to 300 Win Mag (I bought the rifle new in 1996). I am wondering if this action can safely house the 0.550" diameter case of the Remington Ultra Mags. I asked a well respected gunsmith about rebarreling my action to a 300 Norma Mag which is based off of the 416 Rigby and has a head diameter of 0.589". He said that my action is too small in diameter and also said, "I would not recommend the Ultra Mag case either. The Winchester has a 1� diameter barrel tenon which limits cartridge diameter. What happens is pressure expands the case which in turn expands the barrel tenon and even the action. When the pressure subsides all the steel components return to their original dimensions. The brass case can and will at times exceed its yield point and not return to its original size. Then you extraction issues. I think Winchester went to an 1 1/16� diameter barrel tenon on the Ultra Mags."

So one opinion says that I should not use my action for a 300 RUM but Winchester is chambering to the WSM cartridges which actually have a diameter of 0.555". I assume that Winchester must ream out the action a bit more to accept the 1 1/16" diameter barrel tenon for the WSMs so if my gunsmith were to ream out my action the same then I should be able to chamber it to a RUM. Is that correct?

If I can do that what I am actually thinking of doing is to use the 338 RUM case and neck it down to 30 caliber, possibly setting the shoulder back some so that I do not have to seat the bullets so far into the case in order to function in my 3.6" magazine box.

Is the 338 RUM brass relatively easy to find? Is the quality any good?

Appreciate any thoughts or advice, Rufous.

I'll have to make a call to find out for sure, but I believe all M70s through 2006 have the same barrel tenon of 1".. I have a M70 SG .300RUM and it has a 1" tenon with a shank of 1.150"..

I've had several inquiries about using the Rigby or Jeffrey cases for builds and have declined.

The .300 RUM uses the same case as the .338RUM - just necked up.. Or, if you need specific cases N/A from other sources, consider Quality Cartridge in MD for brass..

I opened up the threads on my match rifle to 1 1/16" to get rid of the interrupted thread. Not a big deal...

'Interrupted threads' in general are no big deal on the M70.

That 1" diameter tenon should handle the RUM just fine. It would be the largest case I would consider chambering one for. I had a customer bring me his Classic M70, with the 1" tenon, to have a recoil lug re-attached to the barrel of one chambered for .585 Nyati. To me, that's a little much to ask of that diameter bolt and tenon. To me, that's right up there with converting a Rem 700 to handle the .338 Lapua. It's certainly not that the 700 can't handle the Lapua, it's just that there are actions that are better suited to house and feed that size of a cartridge.

Spot on Malm...

If the RUM can't be tamed with a M70 receiver and 1" tenon, then Winnie wouldn't have brought it to market in the first place..