6mm Super X

[rcw3]

I made up another 6mm cartridge and it shoots great too!

It's called the 6mm Super X and it's made by holding a 6XC sizing die up .120" off its normal position for resizing 6XC cases, and the seater up the same too. You use 243 Win brass, put a little Imperial sizing die wax on the shoulder of the case and run your 243 Win cases up into the die. What you get is a stretch body 6XC that has a body and headspace .120" longer than a 6XC. This gets you away from being limited to using H4350 burn rate powders to try to get 3000 fps velocity with 107 Sierras and 115 DTAC bullets, and allows you to go to powders like H4831SC, IMR7828SSC, H1000, etc.

The neck on the brass winds up .310" long,chamber neck is .323" long) which gives you a longer neck and a 30 degree shoulder angle. You could use a 6XC reamer in long .120" but you would have to trim the brass a little,minimum) but I made up my own reamer for it to avoid any brass trimming.

I use my 6XC dies,up .120" from their normal position) to resize cases and load bullets. I thought that not resizing the bottom .120" of the cases might present an issue, but despite multiple re-loadings, even running some pretty stiff loads, it does not seem to cause any issues so far, but if it does I can pre-size the base of the body of the case once in a while with a 243 Win die if cases became hard to chamber because of not fully resizing down as far as possible.

The picture shows a 243 Win,left), 6mm Super X,center) and a 6XC,right).

Robert Whitley

 

[Austin]

That is very nice.smart idea to do that.what is your accuracy?

 

[Cheechako]

Robert

Not another one

Seriously, yours is very similar to several others that have been discussed on these and other forums. I had a couple of different ones myself.

Let us know how it works and, particularly, what powder and charge weight works best. I could never get 4831 and the likes to give the best accuaracy and kept returning to 4350. In a 30 inch barrel I could get an easy 3000-3100 with the 105 to 115 grain bullets using as little as 38 grains H4350. But that was a fairly low loading density so I had two options, 1) cut the barrel off, or 2)reduce the case capacity. I chose the latter which worked great but what I ended up with was not much different than the new 6 x 47 RAUG or LAPUA, without all the case forming.

I may still cut the barrel off just to see what will happen with the full size case but I'd have to re-chamber the barrel and I'm not sure the results would be any better.

The 6mm Super X is almost identical to Lanny's 243 LSI and maybe he's reading this and can comment too.

Good Luck

Ray

 

[rcw3]

Ray

There really isn't any real work to case forming, put a little Imperial sizing die wax on the shoulder of 243 Win cases with your finger, run the cases up into the resizing die and you're done! I have the 6mm version of the 6.5x47 Lapua, and necking down those cases is just as much work,i.e. put lube on them, run them through the re-sizing die to neck them down).

Maybe the 6mm Super X is a 6mm case in a niche that people don't care to be at, but for a guy that wants to try to run slower powders and not so much pressure to get the velocities up there, this may be the ticket for that shooter. I know I sure like it a lot and I have just begun shooting it.

What's nice is if you already have 243 Win and 6XC stuff, you don't really have to buy anything additional to try it out,but obviously you need to get a barrel chambered up- but you can later set the barrel back to a 6XC or rechamber it to a 243 Win if you ultimately don't like the 6mm Super X).

Robert Whitley

 

[Cheechako]

Robert

Basically what you have is the old 240 Page Pooper from the 1950s. Page made his brass from the experimental 7.62x51 NATO before the Army adopted it and before Winchester started producing the 308 Winchester. He tried to get both Remington and Winchester to adopt it but neither company would do it and Winchester instead came out with the 243 W and Remington introduced the 244 Rem which was really the old 243 Rockchucker of Fred Huntington,made from 257 Roberts brass). Had one of those companies adopted the 240 Pooper we probably would not have seen all the various 6mm wildcats in the last 15 years. OK, you're right, we STILL would have seen them. There ain't a wildcatter alive who is ever satisfied,including me).

Ray

 

[rcw3]

240 Page Pooper - sounds like something you should be buying in the Dollar Store or in some novelty items catalog that makes an unexpected obscene sound.

I don't know what he had for case dimensions, but I just worked off the 6XC dies I had and 243 Win brass to make mine.

Thanks for the info.

Robert Whitley

 

[Raptor]

Robert,
You nearly made my dream case!!! I have been thinking about this ever since Joe was talking about the 6CM. I have both a 243 and a 260 and a 6XC. I would like to use that same case in a 6.5 and see what it would do. I think the 260 has to short of a neck and I like the 30 or 35 degree shoulders on the BR cases. But then again I think the 6MM with the 115 would give you good results and with the slow powders give you good barrel life.

Keep us posted on the results you are getting. When I am ready for a rechamber I may go with something like yours or Joes 6CM.

 

[Cheechako]

Raptor

If you're interested in a 6.5mm version you might want to take a look at the 6.5 Mystic. You can find the designer on several shooting forums usually with the moniker Mystic or Mysticplayer.

Before investing in a reamer on any of these cartridges you might post your interest on the various Forums. You might be able to borrow a reamer for a one-shot chamber job. I have a reamer for the 40 degree version of Robert's 6mm Super X that I'd be happy to lend you and there are both 30 and 35 degree reamers out there with other shooters.

Ray

 

[243Mendoza]

I made up another 6mm cartridge and it shoots great too!

It's called the 6mm Super X and it's made by holding a 6XC sizing die up .120" off its normal position for resizing 6XC cases,...

Your new case looks similar to the .243 Mendoza.

 

[Raptor]

Ray,
Thank you for the kind offer!! I would be intrested in the 30 or 35 degree shoulder if I was to do one. I will keep you info in mind. Thank you once again!!

 

[rcw3]

Part of the reason I did the cartridge the way I did was so I could use the existing die sets,6XC) and brass,243 Win) I have, and not have to buy anything special but the reamer. I could have just used one of the 6XC reamers I have and run it in long .120" but then I would have needed to trim the brass at the neck a little. Actually, if a ran a 6XC reamer in about .140", it would increase the capacity a little more and I would not need to trim the brass at all to use a 6XC reamer, although it would shorten the neck on the 6mm Super X to the neck length of a 6XC.

Robert Whitley

 

[fnnm1]

Robert:

I had all the stuff to make some of the 6 Super X cases last night. The neck is longer and the shoulder angle changed and rounded but that would blow out to look like the 6 XC. A long XC case.

Just curious but what does it gain on the 243 Win for say XTC and Mid range use?

Thanks

Paul

 

[armabill]

I think that the name "240 Page Pooper" didn't go over well with the manufacturers.

A different name might have faired better.

 

[joesr]

Robert,

Great idea! What velocities are you getting from the 115 and 107?

I wont even ask about accuracy as I'm sure it is great.

Joe Hendricks

 

[rcw3]

Robert,

Great idea! What velocities are you getting from the 115 and 107?

I wont even ask about accuracy as I'm sure it is great.

Joe Hendricks

Joe

I have not pushed the upper limit of the cartridge yet, and my initial objective was more for across the course use than anything else. I was looking to burn H1000 as a powder and be able to run 105-107 gr bullets comfortably at 3000 fps, and it will do that without any problem whatsoever. 47.5 gr of H1000 pretty much fills up the case to the junction of the neck and shoulder of the brass and that's about as much H1000 powder as you can practically use,without undue compression). Velocity with 47.5 gr of H1000 and a 107 Sierra, in the barrel I have, is around 3020 fps with great accuracy and close chrono numbers.

In making up the cartridge I wanted to be able to easily use Winchester 243 brass, and my 6XC die set. I also wanted a long neck, a 30 degree shoulder angle, and the ability to burn a powder like H1000, with the ultimate objective of better barrel life with great accuracy and good velocity.

No question my case has a smaller capacity than the 6CM,actually slightly smaller than a 243 Win), and you run out of room to burn H1000 as a powder if you are looking for much more than 3000 fps. At some point I am going to do some testing with H4831SC and IMR7828SSC, but like I said I wanted to start out with H1000 because that is a proven performer and I,like yourself) find it is easier on barrels in a 6mm.

For pure horsepower to drive the 115's, your 6CM seems to have an advantage because of its greater case capacity, and I think in the 6mm Super X to get up in the 3000 fps range with the 115's I will need to use a powder like H4831SC or IMR7828SSC.

I'll keep you posted.

Robert Whitley

 

[joesr]

Robert,

Forget the 7828. It simply does not shoot. I/we have tried it many times in several different cartridges and the accuracy is poor at best.

I, personally, don't know why they make the stuff.

Joe Hendricks

 

[rcw3]

Robert,

Forget the 7828. It simply does not shoot. I/we have tried it many times in several different cartridges and the accuracy is poor at best.

I, personally, don't know why they make the stuff.

Joe Hendricks

Funny you say that about 7828, based on the limited testing I did with the stuff, I think you are correct about 7828, but I have not shot it enough to feel as if I gave it a fair try so I did not rule it out.

Robert Whitley

 

[joesr]

Possibly it makes good fertilizer.

 

[Rtheurer]

Robert

Does Dave Kiff have your Reamer design? I think I may try this baby out. That is if Rock Creek ever gets my barrel to me. I have 200 Lapua Brass waiting right now. A stiller action is sitting & waiting also., thats just not right). I may need some help getting everything set up, if you would be so kind.

I really want the long neck & the 30 deg shoulder. You have made exactly what Ive been tossing around for about 6 months now. Great idea on the use of existing dies.

Russ T

 

[rcw3]

Yesterday I chronographed some 6mm Super X loads with H4831SC and Sierra 107's and DTAC 115's. The cartridge really seems to do exceptionally well with that powder. Here are the results:

43 gr H4831SC, Sierra 107, BR-2 Prime, .010" jump, 3007 mean vel., ES 33, SD 13 -
first shot through cold bore was off on velocity making ES 10 fps larger.
44 gr H4831SC, Sierra 107, BR-2 Prime, .010" jump, 3073 mean vel., ES 15, SD 7
45 gr H4831SC, Sierra 107, BR-2 Prime, .010" jump, 3120 mean vel., ES 14, SD 6

43 gr H4831SC, DTAC 115, BR-2 Prime, .010" jump, 2989 mean vel., ES 11, SD 4
44 gr H4831SC, DTAC 115, BR-2 Prime, .010" jump, 3035 mean vel., ES 16, SD 6
45 gr H4831SC, DTAC 115, BR-2 Prime, .010" jump, 3068 mean vel., ES 14, SD 7

By the way all bullets were plain,NON-MOLY).

I had assumed I would pressure out by the time I hit the 45 gr loads but none of the loads exhibited any excess pressure signs, so it seems there's more to go, but I have no idea how much more.

Today I shot the 44 gr load of H4831SC with the DTAC 115 @ 3035 fps - very very accurate! I am a prone shooter,I shoot with a sling and a shooting coat and no rest or other support), laid down, took two sighters on a target, dialed in my scope, then shot ten shots at another target and came up with a 10X clean,all shot at 100 yards). For me to shoot that well in prone, a rifle has to be shooting .25 MOA or so, since my body movement is usually about .5 to .75 MOA. Usually when a load shoots this well for me in prone at 100 yards, it's a very good 600 and 1000 yard load as well, and the chrono numbers are right too,i.e. good velocity with low ES and SD numbers).

The picture of the cases shows a 6XC,left) with the 6mm Super X,center) and a 243 Win,right).

If I went ahead and set up to have Redding dies made for this, would there be anyone interested?

Robert Whitley