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Hello all, I'm attempting to get an old 8-bore double rifle shooting again. My plan is to develop two cartridges, a round ball cartridge, and a conical cartridge. The bores slug at .847" so I figure a .849" conical but I'm unsure on the ball.
What size ball do you think I should use in a cartridge for a .847" rifled barrel?
Thank you
-Matt
An interesting question!
Round balls don't have much bearing surface for the rifling to grab, which is a side benefit of patching a ball in a muzzleloader. Cap and ball revolvers are often recommended to use groove diameter or slightly larger, but I have an original Colt 1860 Army with bullet mold and the ball is a good .010 oversized, so it shaves a ring and basically makes a short cylinder projectile with radiused ends. Bearing surface is still short but there is a practical limit to what can be shoved into a revolver before the action is over stressed.
In your case, I would probably fit the ball to a fired case, with enough interference that the ball won't slip out easily under recoil from the other barrel, even if that means pressing the ball to final position. You shouldn't see any pressure problems, especially with black powder.
I might consider a partial camber cast of the throat and neck area. Then measure the thickness of the brass cases to see how large of a ball could fit and still allow the case to expand and let the projectile go.
Just off the top of my head, I'd guess .850"
Some pics of the rifle would be great.
Wikipedia 8 Bore search will give you the basic information.
Unless you were planning on using the rifle for dangerous game hunting, I believe I would be using hollow-base conicals.
Quote:
Originally Posted by Matt85
Thanks for the response all!
Sadly, my brass will not be available from RMC for 2-3 months. A fellow forum member on the AHF is loaning me some 8 bore brass so I can test fire the gun. His brass is reamed out to accept a .852" conical for his .850" bore, so it is not going to represent my brass well. I suppose I could ask RMC if they can tell me what the inside diameter of the brass will be.
challenger_i: I have never heard of a hollow-base conical being used in a rifle like this. All of the conicals I've seen or heard of being used historically are solid base with a round nose, ranging from 1150gr to 1250gr.
-Matt
That is true, as the original loads were for dangerous game. I recommended a hollow base slug because you were uncertain as to the correct size. A hollow base in a slightly undersized slug would cure a lot of issues without encountering excessive pressure.
There is a dimensional difference between the 8-bore rifle and 8-guage shotgun cartridges. The rim on the shot cartridge is somewhat smaller than the rifle variant and may cause extraction issues. The shot cartridge base diameter is +/- .015" smaller than the rifle cartridge, and the shot shell you listed is 1/4" shorter than the rifle cartridge.
It is possible the shot cartridge would work for "target" loads, but One would need to be aware of the above stated differences.
challenger is correct, the 8-gauge shotgun brass does not work. I tried some of it from that same link about a week ago and the rim was simply too thin. My rifle actually uses a 3.25" case so the length wasn't a problem. But the thin rim did not hold the case head up against the breech face properly (the cases sit too deep). If I was desperate, I could probably make the 8g shotgun brass work by using solder to thicken up the rim.
I've decided to go with a .850" ball. This should be big enough to get a decent grip on the rifling but small enough as to not cause problems with the case.
-Matt
Enjoy the journey it would be fun to shoot a 8 bore Cartridge gun I would not be beyond using a gun like that to deer hunt !
I shoot a .827" ball out of my smoothbore muzzleloading rifle ahead of 175 grains of 2F. It WILL get your attention! I would go with the .847" ball as it will obturate if it is cast from pure lead.
I suppose it WOULD make a decent brush gun! :)
Quote:
Originally Posted by firefly1957
My thought as well!Quote:
Originally Posted by challenger_i
The only thing that keeps me from using on local deer is that it always rains through our deer season and I'm not big on taking a 128 year old gun out in the rain. I imagine an 85 caliber round ball would do a fine job on anything in North America.Quote:
Originally Posted by firefly1957
-matt
Sounds like a fun journey but there are a few things I would need to confirm. Neck thickness and OD/ID of unfired sized and a fired case. A chamber or pound cast along with bore slug dimensions. That would give me what I needed for first dimension attempts with understanding that obturation is my friend using pure. Also thinking I will would be buying a custom RB mold from somewhere. But hey, it's just gun money! I can confirm your environmental situation, many moons ago I was sent to Boeing Field to take an aircraft apart and put it in big boxes for trip back down here to base. Seventeen days and I witnessed a blue sliver come over one day for forty five minutes worth stopping the rain and or drizzle/mist. How about that green sponge that grows around the bottom of your exterior walls? And I think someone above said pictures please.