New 6mm, 6.5mm, and 7mm short-action magnum

[supersheep65]

I have been looking for a cartridge that can duplicate or outperform the venerable 6.5-284 round in a short-action rifle. So far, I have stumbled upon several, including the 6.5/300 WSM and the 6.5/300 RSAUM. While both of these rounds meet my personal requirements, they burn barrels out very quickly and generate excessive recoil, detrimental to any shooter.

These events have led me to believe that creating my own round/rounds would be the best method.

After much research, I am looking at three sister rounds based on the .338 Lapua Magnum, necked down and shortened. Rather than using a similar case and necking it up or down, I have decided to use a similar velocity requirement and longer or shorter cases.

So far, I have a 6mm round driving a 107-grain Sierra Matchking at 3,250 feet per second, a 6.5mm round driving a 142-grain Sierra Matchking at 3,250 feet per second, and a 7mm round puhing a 175-grain Matchking at 3,250 fps as well. All three of these will fit in a standard short action.

Input from long-range precision shooters, reloaders, benchrest competitors, etc. is greatly appreciated.

 

[mikecr]

Of the 3 bullet's chosen, the 175 has a slight edge in BC, and could reach those velocities with lowest pressure in short cases. But it would take alot of powder, and recoil would be higher. Definitely alot to account for.
Toughest would be predicting accuracy at 3250fps. In the event that 3200 doesn't produce, it's possible with such a case that you may never realize best accuracy at lower velocity..Then your stuck.
Shortening cases is easy with forming dies, but brass gets really thick, really fast in doing this. Just look at a WSSM case & you'll see what I mean. It's so damn thick because it was formed from WSM brass. I turn necks on a 6.5wssm from .0195" to a reasonable .0125" thick. It's alot more work than I thought it would be. Mix n matching mandrels, 2 annealings, several neck changes up and down.

I know none of this helps, but I thought I'd highlight things to consider in your plan. You may even consider a backup plan, based on something easier.

 

[6Dasher]

Hi SuperSheep,


What kind of rifle is it for? LG, HG, hunting/carrying? How much extra do you need over the 6.5-284?


jim

 

[jb1000br]

Hmmm...

BIG bolt face eliminates vipers/pandas.

Brass forming = PITA

Not that much speed is required.

Might as well do a 6.5 WSSM, or a 6mmWSSM or a 7WSM...

JMHO, and YMMV,
JB

 

[Wild_Bill]

if the 6.5-284 is too hard on barrels for you just use a 6.5x55 or a 6.5x55AI and dont look back. I assume a light gun capacity or hunting case?? if so a 7mm SAUM or 7mm WSM work verry well the slight edge to the WSM using Norma 300 cases necked down and turned you can also improve the cases if you like. I do not see any use designing a shortened case off a 338 Lapus because there are so many good cases to just do minor changes to like necking up or down and improving. A verry good 7mmm is on the 8x68S RWS case improved. Awsome For a Heavy gun. Look at the cases made buy Lapua, RWS and Norma in that order and you might find a better design without having to shorten cases and go through the trouble of thick shoulders and necks. Unless you cut the shoulder section of the case off then turn the case sides on a mandrel you will always have trouble with shoulder thickness neck thickness can be controled with neck turning but you cant neck turn the shoulder. Hope this helps JMHO.

Cheers Bill
Australia