Anyone have experience reaming a 7mm rem mag for 300 win mag casings?

Bigbones139

Bigbones139

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Am looking to get and extra bit of case capacity and was wondering if you could ream a 7mm rem mag out to use 300 win mag casings for the extra capacity? Also if i do it can i just use 7mm rem mag neck sizing dies on 300 casings to form them or is there special dies i can get to do this in full size? Any help or info on this subject would be greatly appreciated!
 
I'm sure its been done. There is the 7mm Shooting Times Westerner, based on a full length belted case. A 8mm Rem. Mag. could be necked down. Check the established reamer makers, like Dave Kiff at PPG, or with Clymers, and see what they have listed.
 
Thanks for the reply tiriaq.... I figured somewhere someone had done it... Any body else have any experience?
 
Ohhhhhhhhh Yea

From the point of what will you gain, NOT MUCH, it's been done.
For the money involved, you would be further ahead to buy to buy a rifle in 7mm ST Western. To rechamber a factory barrel doesn't improve accuracy, and you will have a wildcat caliber, very hard to sell. When a rifle is rechambered one of the first things to look at is the barrel, is it a new custom barrel or is it the factory barrel rechambered (which I wouldn't touch).
Take care and enjoy Bill
 
Its an aftermarket shilen barrel and as for resale it makes no difference to me as this is for me and i have no intentions of selling it... Passing to my kids down the road yes but selling no! The accuracy is top notch and i wouldnt expect or need it to get better... I just want a lil more ooooomphhhh and totally understand its a wildcat and thats what i am after... Maybe quirky but i hate having what everyone else has... My mag isnt long enough to accept a stw casing so that out and the gun i have is what i want just with a bit of an advantage! Thanks for the info though
 
I did the same idea only in .264. Still working on loads but it looks promising..

it can be done and can be gratifying to..

I believe the cartridge you are looking for is a 7mm Mashburn Magnum..but I'd have to check my P.O. Ackley book to be sure..
 
Necked down bigger cases require longer barrels to get that extra "ommmphhh"

If the barrel is not at least 26 inches I would not bother... Preferably 28 inches...
 
The barrel is 28" Guntech that is why i am even considering this and it is also a real tack driver!


Blygy... Thanks for the positive info... Glad i am not the only one with these crazy thoughts...lol 264 was actually another consideration i had for another action i have on hand if the 7mm worked out but i thought i would start with it as it has a shilen barrel already installed... I am quite interested though in your progress with the 264... I beleive the long range ability of the 264 with say a 160 grain if you could push it fast enough and have the proper twist could be something amazing!
 
Bigbones139 said:
The barrel is 28" Guntech that is why i am even considering this and it is also a real tack driver!


Blygy... Thanks for the positive info... Glad i am not the only one with these crazy thoughts...lol 264 was actually another consideration i had for another action i have on hand if the 7mm worked out but i thought i would start with it as it has a shilen barrel already installed... I am quite interested though in your progress with the 264... I beleive the long range ability of the 264 with say a 160 grain if you could push it fast enough and have the proper twist could be something amazing!
Click to expand...

It sounds like it is a good candidate for the STW... probably cheaper dies that way and it would get great velocities. The barrel may require setting back slightly to clean up the old neck if it is larger in diameter than the STW reamer... that sometimes happens...
 
The 300 Win necked to .284 is often called the 7mm Yukon.
A local guy here has one. The neck gets pretty short when necked down from 30 to 7....but it does work, I shot it years ago...a 150 at 3350 ish IIRC....
 
As Rick points out, known as the 7mm Yukon, and the 7X66 Randall. You will not achieve 7 STW velocities (smaller case), but you will be slightly faster then the 7 Rem Mag. I would personally go for the STW, particularly with a 28" barrel. Most full length actions can be made to work with a the full length H&H case. If not, and you want something slightly different, go with the 7mm-300 W, the animals will never know the difference. - dan
 
The 6.5mm based on a 300 Win Mag has been done - I did it.

The 7mm can be done the same way. Run a 300 Win Mag case into a 7mm Rem Mag die that has been adjusted up the correct amount (about 0.125") to account for the longer case. You're done. You can neck size with the 7mm Rem Mag Neck-Sizer.

You'll need a reamer of course. Do up the required 2-3 cases fitted with your bullet of choice seated to the OAL you desire, and send them to a reamer manufacturer, according to their instructions - I like Pacific Tool and Gauge.

You'll see very modest gains. You're adding 8-10 grains of powder capacity and should expect no more than another 100 fps.

I'm going to clarify this common statement:

guntech said:
Necked down bigger cases require longer barrels to get that extra "ommmphhh"

If the barrel is not at least 26 inches I would not bother... Preferably 28 inches...
Click to expand...

It's true that large capacity cases gain more velocity per inch of barrel added than smaller, but the notion that, for example a 7mm RUM with an 18" barrel is no faster than a 7mm-08 with an 18" barrel is nonsense - it will be much faster. A 7mm/300 Win Mag with a 22" barrel will have a MV somewhere around 75-100 fps faster than a 7mm Rem Mag with a 22" barrel. With a 28" barrel it will be somewhere in the order of 100-125 fps. They don't require longer barrels - the larger case will be faster at every barrel length. However it is well known that the larger cases add more fps per inch than the smaller.
 
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