7MM/6.8WESTERN

[John T]

Hello.
This topic may have been discussed previously, but has anyone developed and tested a 7mm wildcat of the 6.8 Western? (Rod, I will not believe that you have not!)
The 7RSAUM is busting its guts to get to 3500 ME. The 6.8W case, with about 4% more chamber capacity, should achieve that comfortably with the largest of 7mm projectiles. It also has an extra 0.02 of shoulder-to-mouth which helps a little with long bullets.
Of interest is that the CC of the 6.8W is about 3% less than the 300WSM and should make it more efficient than that case for .300 and .276 bores.
Regards,
John Tracey.

[John T]

OK.
Seems that no one has tried the 7/6.8 or will not say so. I accept that a Winchester case with 0.020 rebate is less than idea, but what else is wrong with it?
Regards,
John T.
8.7.24

[Frank Green]

I'll take a stab at it but first what is your intent on using the round for? F class? Hunting?

I think the first issue is going to be getting the 6.8 Western brass. Being as Winchester is the only one making it currently to my knowledge isn't going to help wildcat it etc...

The extra case capacity also means it will be harder on barrels.

If your muzzle energy limitations are 3500 in Australia and as you say the RSAUM struggles to reach that energy limit which puts you around 2950fps... if I'm mistaken or not following you correctly please correct me.

Why not just take the 6.5PRC and neck it up to 7mm? Several places are now making 6.5PRC as well as ADG is making box 7/6.5PRC brass so you don't even have to neck it up and when loaded you can easily push 180gr bullets to 2900+fps from a 30" to 32" barrel on a F class gun.

The 6.8 Western has a case capacity of water around 74gr. The 6.5PRC case is around 64gr so for the 6.5case to be able to push a 180gr bullet around 2900+ it's using less powder / will be more efficient. I'm loading 57.0gr of N555 and running 183smk at 2940fps out of my gun.

I think your brass supply will be the main issue with the 6.8Western right now. Even for us here in the States it will be an issue.

Later, Frank
Bartlein Barrels

[John T]

Hello Frank.
As always, a generous contribution.
F Open was the intended use.
But I have made a serious blunder! The shoulder-to-mouth length of the 6.8 Western is only 0.4365, far too short of what I regard as the minimum of 0.5 (boat tail 0.25 + neck grip 0.25). So, forget it.
If Winchester were to make a .308 Western with the same powder chamber but with a 2.1 OAL, that would be interesting.
I have looked at the 7-6.5 PRC, but do not see it as a replacement for the 7 RSAUM. On first glance, it seems to me that the PRC has a smaller powder chamber than the SAUM. Yet your load in your PRC will drive the 183 at 2940 MV to above 3500 ME.
A simplistic question is, how does your 7RSAUM 183SMK load compare to your 7-6.5 PRC 183SMK load, for accuracy?
Kind Regards,
John T.
10.7.24

[John T]

Hello Frank.
I forgot that the 6.5 PRC is based on the 300 RCM. That case has very thin walls. This results in a powder chamber capacity which is larger than in another case with similar or even greater outside dimensions.
Relying on the dimensions in the "Load From A Disk" drawings for the 300 RCM and the 7 RSAUM, I have calculated that the powder column capacity of the 6.5 PRC is about 2.7% larger than the 7 RSAUM. That is consistent with your 7-6.5 load outperforming the Saum.
Hornady is not renowned for producing match grade brass. But you say there are other manufacturers and even one making 7-6.5 PRC brass.
Shoulder-to-mouth of 0.4613 is less than the 7 RSAUM, 0.497.
Whilst case life of this thin-walled case may not appeal to some, the 7-6.5 PRC might seriously challenge the 7 RSAUM.
Regards,
John Tracey.
22.8.24