complicated reloading question

[mjbgalt]

i really like the 6.8 but i was thinking...for better downrange performance, wouldn't i be better off by necking it down to 6.5 or 6mm for the better BC and higher velocities? why make it a shorter, stubbier .277" bullet when a 6mm of the same weight would be longer? and if i did this, would it increase pressures?

-Matt

[stimpylu32]

Matt

Need more info , what type rifle are we talking about here and how do you plan to shoot this ? will it be a 6.8 chambered barrel or a new barrel with a new chamber cut to fit this new case ?

If you plan to just neck down and shoot a 6mm bullet in the 6.8 barrel your acc will probably stink as it will be way too sloppy for the rifling and your brass life will be gone from working back down that often .

As for the pressure that is going to depend on what and how you work this new round .

stimpy

[mjbgalt]

lol, of course i wouldn't shoot a 6mm bullet in a 6.8mm bore...was thinking more along the lines of a 6x47 barrel cut for a new cartridge...a 6mm SPC, for lack of a better name.

just neck it down and shoot .243" bullets in it. i was thinking that would get me very close to .243 ballistics while still being able to shoot it in my G2 Contender rifle.

-Matt

[Grumulkin]

I can't imagine that there will be any advantage in doing what you propose.  If you take a bullet of a given weight and, one made for a 6.8 mm rifle barrel will have less bearing surface than one made for a 6.5 mm barrel so yes, pressure will be increased.  You will have to lower powder charges which will lower pressure to an acceptable level and that will lower velocities probably canceling out any theoretical advantages of a higher ballistic coefficient.  Also, getting a barrel made to your proposed specifications will be expensive, you will have to make all your own ammo (maybe you do anyway) and if you ever want to sell your barrel you might find no one wants it.

But...shooting enthusiasts have wildcat cartridges made up all the time and consider it fun.  If you don't care about expense and practicality, go ahead and experiment away.

It cracks me up; people get Contenders and then want a cartridge made to perform like an Encore.  They get a 300 Weatherby Magnum and then want loads so it won't kick any more than a 30/30 Winchester.  I say, if you have a Contender, be content with what the Contender can do and it can do it all without a lot of agonizing about coming up with a new wildcat cartridge.  There are a bunch of good Contender wildcat cartridges already designed (see the web site of SSK Industries).  With them, you can use a Contender to take any animal from small varmints up to and including elephant.

[stimpylu32]

Matt

The only possible advantage here would maybe be bullet choices as far as weight and shape ,as far as ballistics i see no real improvement , I'm sure someone has done this as a what if round but i can't see any real world advantage  .

You may check Ammo Guide and some of the other sites for something that has a better track record with out all the work of a new Wildcat .

stimpy

[mjbgalt]

i really like my g2 and it fits me well. i was wanting something both unique and also effective.

i don't expect it to shoot like an encore or be something it's not.

-Matt

[Grumulkin]

One other point, if a bullet of a given weight is made in a smaller caliber, it will have to be longer.  A longer bullet will need a tighter twist to stabilize it.  The twist of the Contender barrel may not be tight enough at the velocities obtainable to stabilize the bullets.

New ideas are great but I doubt this is a very new idea.  I certainly don't care if you do it, by the way.  My dream is to have an Encore handgun made up in 375 Weatherby Magnum or maybe 416 Remington Magnum; not what a lot of people would call smart or practical.  So, really, go for it if you want to and have fun.  I'm only trying to point out what I perceive to be flaws in your plan.

As far as bearing surface goes, if you take say bullets weighing about 160 grains in calibers .308 and .284, the .284 caliber bullet will have a longer bearing surface, a higher ballistic coefficient and will require more pressure to move it down the bore.  The point I was making is that your quest for better performance via a higher ballistic coefficient would probably be frustrated because you wouldn't be able to obtain as high a velocity at acceptable pressures.  The only thing ballistic coefficient gets you is better retained velocity which is good but if you have to start out slower to begin with, you've gained nothing.

[Graybeard]

If you want a 6.5mm I'd go with the already world proven 6.5 JDJ and there is a 6mm version also if ya just gotta have that small a bore. I definitely don't think you'll improve performance by dropping to the 6mm however.

The little 6.8SPC case isn't very large to begin with barely larger than the .223 really so there isn't a lot of extra case capacity to work with. With zero pressure tested data to go on you're treading dangerous waters in my opinion with it in the G2 as you have no way to know what kinda pressures you're running. The JDJs on the other have have plenty of pressure tested data available for them.

To my way of thinking the 6.5 JDJ and the 7-30 Waters are as good as it gets for the Contender in the smaller bores and there is enough good book data for them so you can be sure you're not stretching the frame.

If you just gotta have a wildcat no one else in your neighborhood has already then go for it but as with any new wildcat you're out on a limb for safe data and the Contender is a bit of a weak platform for going out on that limb without tested data. Yes for sure with the smaller bore and same weight bullets pressures will be higher. How much is the question and sadly there are no answers floating around for it.

[mjbgalt]

true, not enough pressure data. i am experienced in loading but not in creating totally new cartridges.

i will look into the JDJ rounds. i wanted to get away from having to fireform and buy a lot of new stuff...but it looks like this is going to be a little more complicated than i expected.

thanks for the input guys!

-Matt

[Graybeard]

You'd still need to do that with the rounds you proposed. It's no more complicated a process with the JDJ rounds than it would be with the two wildcat rounds you are thinking of. At least with the JDJs they are now standardized and dies are available from SSK made by either Hornady or RCBS. With what you proposed you'd have to get someone to make up the dies especially for you at far higher cost and then make sure that your barrel maker and die maker both were using the same specs for it to work properly.

[jhalcott]

  If it is true that the 6.8SPC was developed as a replacement for the 5.56 military round,you'd be reinventing the wheel doing what you propose. BUT if the good doctor wasn't curious we wouldn't have the EXCELLENT 6PPC cartridge.!

[bubbadoyle]

I could be wrong but wouldn't this be the same as the 6mm tcu?

[Graybeard]

I could be wrong but wouldn't this be the same as the 6mm tcu?

No not really. The 6.8 case is a wee tad larger in diameter than the .223 case not by a lot but by a little so it does have a few grains more capacity.