Goldilocks 6mm between 6CM and 6UM?

[Arithson]

What

Funny I just saw this thread, I'm in the process of designing just such a 6mm..
View attachment 709183

What ya got there?

 

[khuber84]

What

What ya got there?

Kinda looks like a 6sst?

 

[Arithson]

Kinda looks like a 6sst?

That’s what I was thinking. Thats been creating an itch I may need to scratch

 

[khuber84]

That’s what I was thinking. Thats been creating an itch I may need to scratch

I'm personally not a fan of Sherman anything, but a short mag with a 1.920 case length(similar to creed) and a neck that's about 0.270 long, 30 degree shoulder, 0.010"/1.000 taper, would hold 65ish grains of powder, be like a short action 240wby.

 

[762 ULTRAMAGA]

What

What ya got there?

6.5 prc necked down and the shoulder bumped back .140"
The case capacity is just under 62 grains, I'll give it a 40 degree shoulder so it'll probably end up around 63.
The longer neck will allow 115 vlds to be seated above the neck shoulder junction, and will also work with 108s

 

[AZ_Hunter]

I think Shawn's 243 Terminator would probably get you there. He gets around 3300 from a 26 so 3000 from a 18 would probably be attainable or damn close to it. Shawn has dies and Lapua formed brass you can buy also which makes things nice and easy.

243 Terminator

You have entered the home of data for the Terminator family of cartridges. Like all loading data this is just a guideline to help you and not absolute information. This is simply what worked for us in just one or two rifles with our lot of powder, bullets primers etc. It is still your...

defensiveedge.net

I looked at the site and maybe I’m just blind, but what case is that cat based off of?

 

[rifletuner]

If I was starting from an absolutely blank slate, I would go 6PRC. But I have decided for me, the easiest choice is a 6/284. And thats because:

1) I have a standard boltface Tikka as a donor action already; and
2) I used to shoot a 6.5/284 match rifle, and still have my old loading dies. The FL die is a Redding bushing die and I have plenty of 6mm neck bushings I can use, and the seating die is a Wilson Arbour die, so I just need to change the seating stem to 6mm.

An extra bonus is that I can use Lapua 6.5/284 cases.

I am just debating if I rechamber a low round 6XC barrel I have already, or go to a lighter profile in a new barrel. But otherwise the decisions were pretty easy to work out.

 

[khuber84]

I looked at the site and maybe I’m just blind, but what case is that cat based off of?

243win, and I don't think 3300fps is possible with heavies, maybe running sub 100gr bullets, or the 105 Berger and a case stuffed full of rl26. I know a 6cm topped of with rl26 will do 3250, but it's not very smart to run at top end.

 

[solarshooter]

If I was starting from an absolutely blank slate, I would go 6PRC. But I have decided for me, the easiest choice is a 6/284. And thats because:

1) I have a standard boltface Tikka as a donor action already; and
2) I used to shoot a 6.5/284 match rifle, and still have my old loading dies. The FL die is a Redding bushing die and I have plenty of 6mm neck bushings I can use, and the seating die is a Wilson Arbour die, so I just need to change the seating stem to 6mm.

An extra bonus is that I can use Lapua 6.5/284 cases.

I am just debating if I rechamber a low round 6XC barrel I have already, or go to a lighter profile in a new barrel. But otherwise the decisions were pretty easy to work out.

I'm considering 25-284 for these same reasons. I like the 25 for the higher wind number and still plenty of speed from a suppressor length barrel.

 

[joshr]

Fire forming the 6UM is very easy, but the 6 PRC is a fine option if you want to avoid that.
Either cartridge can be put on cruise control with H1000 and lighter bullets. Not sure what the difference would be over the life of the barrel but probably 100 rounds at least vs high pressure N570 loads.

Sorry to revive a old post but what sort of speed would you expect in the UM with h1000?

I want a fast 6 with decently heavy pill but we can't get VV powders here.