.684 bore, what diameter ball?

[Canute Rex]

I just bought a repro matchlock smoothbore made by John Buck and I am trying out various ball sizes in it. The bore measures .684".

I bought some .662 balls and tried them, but I had to patch with some very thin material and it tended to tear. The bore is like a mirror, so it's not internal roughness. A friend offered up some round balls he had cast in an old bag mold. They were kind of oval and rough, .64~ to .65~, but they went down the barrel in .025 ticking easily. I just dovetailed in a front sight and I'm still figuring that out, so no solid idea about accuracy yet.

It seems impossible to find a used Lyman .648 (discontinued) mold, so I am considering buying a custom mold from Jeff Tanner over in the U.K. The question is, what diameter?

The .648 to .650 range corresponds to 17 gauge, .662 to 16 gauge, not that it really matters.

Smoothie shooters, please weigh in. Thanks.

[Collector]

A good place to start and recommended by many as a 'standard' is .020 under (miked) bore size.    Good luck!!

[D. Taylor Sapergia]

My John Manton double percussion shotgun has a .687" bore.  I shoot 15 gauge shot stuffing out of it, and for a round ball, it likes .650" ball from my Rapine mould, and a .020" ticking patch with mink oil.   So, consider a .030" undersized ball and a nice substantial patch.  The thicker patch carries more lube, gives a tight seal and does not require cleaning after any number of shots.

[Daryl]

Canute - I assume the crown of your musket is very sharp, otherwise the thin patch would not have torn. Something has to tear the patch - merely  being tight in the bore won't tear the patch.

Follow Taylor's advice on using a thick patch with appropriately sized ball.

A .662" ball should be OK in a .687" bore (that's .025" smaller) with a .015" to .020" patch IF the crown is smoothed to allow entry.  If you don't touch the crown, you'll need a thinner patch or smaller ball, but nothing thinner than .015" should be used. As Taylor said, the patch has to hold enough lube to do it's job of cleaning while loading, and depositing enough lube on the bore's surface to soften that shot's fouling.

Taylor has forgotten, I think - the bores on his Manton run .675" and .0677"- a true 15 bore gun.  They are both slightly belled at the muzzle. The smaller size (than his remembered .687") is why it seems to prefer the .650" ball, being .025" and .027" smaller than the bore.

I shoot a .0215" patch with a .595" ball in a .62".  That is .025" difference. Taylor uses a .605" ball in a .620" bore, that is .015" difference. He is using a .019" patch with that load.  A number of the guys at our club use .600"s in their .615" and .620" smoothbores along with ptches running .018" to .022".  No one has to wipe the bore during a day's shoot.

[Canute Rex]

Thank you, gentlemen.

In fact, the crown is more like a 45 degree chamfer, and a small one at that.

I'll start by rounding the crown and trying a few more .662 balls with various patch thicknesses. It would be very convenient to be able to use .662 because I can get a standard Lyman mold for that.

[Daryl]

Jeff Tanner in England will make you any size you want for under $40.00.  Tanner moulds fit RCBS or Lyman handles.  I have 5 of them.