12ga smoothbore round ball accuracy?

[HWooldridge]

At that point, it's easier to just make the walls full diameter and have a slug shaped projectile, as illustrated in post #48 above.

[Barry54]

I read some declassified papers a while ago, where the US military in the sixties had copied various Soviet Union missile designs, based on pictures from Soviet military parades on The Red Square.
The designs were then tested in wind tunnels and were found to be quite effective, though sometimes odd looking. A test was also made on the design of the Vostok landing module - which is basically a truncated sphere - and it proved to be remarkable steady due to the center of mass being moved forward.

A truncated full bore lead ball would weigh about one ounce - depending on how much "trunc" it has - and should remain stable in flight if fired from a cylinder barrel.
The ball could be made a tad overbore to ensure a tight fit throughout the journey down the barrel (it wouldn't take much force for the forcing cone to swage it to size)
The flat base would probably work great on top of a felt wad, sandwiched between two x12x seals.

I promised myself I would stop with the slug-mania and concentrate on more important stuff, but I must admit - it could be interesting...

Thanks for sharing this!

It wouldn’t be terribly difficult to get an existing round ball mold machined down to get there. It would also solve some problems with wads wrapping around the ball.

What is the optimum amount to remove?

[Cap'n Morgan]

What is the optimum amount to remove?

I'm not sure.
If you imagine the shape as a bowl and turn it upside down, its obvious that the "bowl" will be more stable the lower it is. But this is a static stabilization.
The drag on the ball in flight will determine where the actual pressure point lies. Calculations like that are way beyond my humble abilities.

You could try a simple experiment with what you already got. Just file a flat on the round ball with a rasp file, and load the ball in the wad, flat side down.
Maybe also try loading with the flat in various positions in the wad, and compare the groups. It should at least document the Bernoulli effect* on the balls in flight.

* To watch the Bernoulli effect in action, take a look at this video of a couple of guys dropping basket balls from a great height.
Notice the dramatic increase in drift when the ball is given a spin when dropped

[longbow]

The Balle Nessler is sort of the same principle... short and stubby



They were apparently quite accurate in smoothbore muskets. I made a clone mould for my 12 ga. slug gun but got mixed results, mostly decent accuracy but some wild flyers too.

Longbow