I have a Savage 300WSM that's always sitting in the safe. Because I shoot varmints all the time I was going to buy a second barrel and use it for long range critter blasting.

My idea is to build a 6mm Cat off of a WSM or SAUM case because then I wouldn't have to change the bolt head or magazine.

The 243 Win case holds about 54 grains (H20)and I'd like to get about 10% more velocity. Using the old 1% velocity for every 4% case capacity calculation, I figure that I need a case that holds about 75 grains of water.

The available short fat case sizes are:
6mm WSSM = 50 grains of H20 (Comparison only)
7mm SAUM = 73 grains of H20
7mm WSM = 79 grains of H20

The issues are that Winchester said that they could not get the big WSM case to work well with the 257 cal because of the expansion ratio and the SAUM is doing so poorly in the marketplace that you have to consider case availabilty in the future.

So what do you guys think?

I has long been my impression that for a 6mm bore any cartridge with a capacity greater than a 6mmRem is "inefficient", and anything bigger than a 6mm-06/240Wby
is only useful in consuming more propellent to go the SAME velocity.

It's kinda like the Big 22's, the largest practical 22CF is the 224Clark and that is ONLY practical with 70gr and 80gr bullets (a 224Clark is a necked down 6mmRem)

Can you build a 6mmWSM? sure you can.
Will it achieve your goal? mabey, with the heavier 6mm Bullets.

Will that barrel have a short violent life? yup.

Granted I'd love to see a Woodchuck on the receiving end of a 70gr Nosler launched at 4200fps, but I personally wouldn't build a rifle that is unlikely to survive launching 1000 of them before the throat was gone.

you may feel differently about the speed justifying the short barrel life...

The second time I burned up a 25-06 barrel buring up barrels for the sake of doing so got tired....

AllanD

The 30.06 holds about 69 grains (H20) and that's why I was considering the 73 grain SAUM case.

This gun would be for the 115 grain bullets pushed to about 3200-3300 fps strictly for 600-1,000 yard shooting.

Frank, your Idea isn't bad at all.I once built a 6mm-.270 Imp that with the 115 gr. original Barnes' bullet was a great mule deer killer. It is still used every year in Colorado since 1967 or 68. That's a while ago.

It also was accurate out to a measured 476 yds.

Satisfy your whim and look back later if there was something to be learned. roger

Australia's "gun guru" Nick Harvey published an article a few months back on the 25WSM and reported very erratic behaviour with some powder/bullet combinations. Examples in the article include a 100gr load chronoraphing at 3500fps with normal pressure, followed by the same load with extraction problems and 200fps less with smoked and dented cases, followed by a third shot at 3600fps and also smoked and dented cases. Might be worth a rethink using the short/fat WSM cases.
Cheers...
Con

I would like to do an ultra light in 6.5 RSUM. 1000yards guys are reporting good results. 6mm might be too much of a good thing.

You might consider a .257 or a 6.5
I know you want a 6mm Nut thats a lot of powder and a small hole for the preasure to escape from. Jon sundra did a wildcat .257 saum on a howa an it was real good for him. Hell buy 300 cases and you would be set, if you ran out you couls allway run a wssm reamer in later. ...tj3006

scuse me I did not proof read my last post, I typed nut when I ment now !

I am expecting delivery of my 6.5 WSM On a Remington action and Jeff Lawrence #5 contour 26" barrel. I will report results as soon as i can get it broken in. I plan to shoot 120 TSXs and 142 SMKs.

Stay tuned - I'm keeping my fingers croseed that it does what I expect.

Don't think that the 1/4 theory goes on forever. At some point there has to be diminishing returns.

You can change the bolt face on a Savage.

Your barrel will burn out before you know it.

Check out the 244 H&H Magnum for it's results.

I just got my 6mm wsm a few weeks ago. So far i love it. It was very easy to get a load work up for it. Just about everything i tried worked great. I had pac-nor do a 3 groove 12 twist 29"barrel. I will be using mine mainly for whitetail deer, so i loaded up some 85gr barnes xlc's. I found 72grs (i think thats right)of Ramshot magnum to be the most accurate with 6 shots under a dime at 100yrds. The speed was +3800fps. at 15'from away with an oehler 35. No high pressure signs in this gun or any weird stuff. I used winchester 270wsm brass and ran it through 3 redding bushing dies. The case necks were a little tight,but it shot so well i didn't bother to neck turn and it didn't seem to cause any problems. I also have a 243wssm and the best (saftly) it will do with the same bullet is about 3350fps and that is with about 50grns of powder. So for about 20grns of powder the 6mm wsm picks up about 500fps. I dont know long the barrel will last but it should last me a lifetime and if it doesnt, thats what they make more for.

Frank, I would go w/ the SAUM as well. Buy 500 cases & you will probably burn the bbl. up before you use the cases up.
My choice for a hot 6mm would be the 6x284 but I understand you want to keep the rifle as is & swap the bbl. only.

Frank, If you have a plethora of rifles and use them all as needed or desired, you will never shoot a barrel out. That 6mmX .270IMP I previously mentioned probably hasn't average more than 10 shots a year for the last 36 years. It was and is a deer hunting rifle.

Now the other thing going for a sensable shooter is that he will tailor his loads for specific use. That means a large part of the time the ammo will be down loaded. Now if you are as old as I you probably will die or suffer from dementia before you can shoot out that barrel.

Hell! If you don't go for it you will only look back in regret later. roger

Thanks guys, I have a 6.5x284 and all of the 22 centerfires that I can use right now. So I figured with the short action, magnum boltface already set up for the WSM cartridge I'd play on a fat case with a 6mm.

I'll probably go ahead with the 6mm SAUM and see how it flies.