Recently started casting my own roundball, they have a sprue on them. I am going down to the range tomorrow with my Walker, would they be safe to shoot with the sprue, I have only ever shot roundball without a sprue.
The sprue is fine as long as the ball is loaded in such a way that the extra material isn't going to be sheared off by the mouth of the chamber.
Not that shearing off the excess lead would create a safety problem. It wouldn't.
Shearing off the extra lead would take extra force on the loading lever though and the extra force needed could damage it.
Just make sure the balls are slightly larger than the chambers. The larger balls will shear off a little lead making them exactly the same size as the chamber.
This is necessary to keep the flame from the firing chamber from lighting off the powder in the adjacent chambers.
It is also necessary to keep the loaded ball in the chamber from moving forward, out of the chambers mouth, when the gun recoils.
If a ball moves out of the chamber it can lock up the action when the hammer is cocked for the next shot.
They were designed to shoot round balls. Bullets or "conicals" as they're called were adopted later on.
Actually bullets in original Walkers were a bad idea because of the pressure increase with their use.
Walker's had a bad reputation for burst cylinders because they were made of iron not steel and was the main reason for their large size.
Though a micrometer is much more accurate than dial calipers for measuring the diameter of round balls, it sounds like the OP could use a good set of dial calipers to find out what size his chambers are in the Walker and also measure the ball size.
It would be interesting to know what size of casting mold you have. That would give us a chance to figure out what the balls would be used in.
As we are only talking about the balls needing to be a few thousandths of an inch larger than the chamber you might have the right sized mold but the lead alloy is causing the trouble.
Some alloys shrink more than others when they cool.
On the other hand, it's possible you have a ball mold that's made for use in a single shot gun.
Typically, a single shot gun will be loaded with a patched ball so the ball is smaller than the bore size. A .45 caliber single shot would use a .440 or .445 diameter ball.
A .44 caliber cap and ball gun on the other hand should be using a .451 to .457 diameter ball.
The thing to remember about muzzleloading guns is, the caliber or size is the size of the actual bore. With a rifled barrel, the rifling will always be larger than the bore size.
For instance, a .44 caliber 1860 Colt reproduction will have a bore size of .440 but the rifling size could be .452.
That .452 diameter is the reason the chambers in the cylinder and the ball size will be somewhere in the .450+ size.
Gus is right about a mic being more accurate for measuring round balls but that being said I almost never use a mic as I've gotten so used to using my calipers.
I only need my digital Starett mic for ten thousands reads as after using a caliper for so many years I can hold .0005 for outside reads (half a thousands)with my dial caliper regularly which is more than enough accuracy for most gun work.
For inside reads I use a split ball gauge and the calipers.
I've got several of the same brass presentation molds in .36 & also .44. I used the .36 mold as a kid, to cast the thousands of RB's used in a Colt 1861 Navy. I went on to later cast using various Lee RB molds & have several rifles & revolvers that have never seen anything but cast balls.
The Lee mold cutter leaves minimal sprue nub & loaded either up or down, doesn't much matter.
for a test I dry balled .451 hand cast balls in the cylinder of an 1851 Pietta .44 Navy. Sprue up, sprue down and sprue on the side. The balls were knocked out through the nipple hole with a brass punch.
In every case there was a nice wide band sealing around the ball.
I cannot speak for accuracy these guns are used shooting CAS and accuracy is not a problem.
My thought is "sprue it! stuff 'em in and let fly".
but that is just me.
To the op, when the ball is the right size it will as said shave a ring of lead off the ball. The rammer has a round cup in the end to fit the ball size. It takes a bit of pressure to ram home. The sprue mostly gets rounded out when rammed.