How To Calculate Proper Ball Size

[Rokon]

WHOA! Thank you all. But after reading the use of drill bits as pin gauges and using drill press turned hardwood dowels as a measuring tool, my whole approach has turned around.
In other words, if we can gauge the land-to-land diameter of the barrel with a drill bit or shaved down dowel, then that's the ball diameter. What's left is the groove depth which will be filled by a proper thickness patch reached by experimentation.

Is my thinking and that conclusion based on your recommenations correct?

Please comment!

 

[Zonie]

No. The land to land distance is the bore diameter. Not the ball diameter.
If you are going to shoot balls, you must use a patch with them so some clearance must be made to allow the patched ball to fit into the bore.
The accepted norm for the ball size is .010 smaller than the bore so, a .50 caliber bore will use a .490 diameter ball.
The patch thickness may vary with each barrel but it must be thicker than the rifling grooves depth to provide the sealing needed and to grab the rifling grooves.

In a rifle, the patch thickness most often used by shooters on the forum is about .018 thick. When this thickness of patch is used in the .50 caliber barrel I mentioned the combined size of the patched ball will be .490 (ball) + .018 (patch on one side of the ball) + .018 (patch on the other side of the ball) = .526".

 

[Rokon]

Zonie--I follow you, but please help me get my head straight.
Rather than making a bore cast or using an oversize ball rammed into the muzzle, are we saying that one could use a drill bit shank as a pin guage or a hard wood dowei turned to slip just so into the muzzle to determine land-to-land diameter. Having the land-to-land diameter we could subtract .010-0.20 for the proper ball diameter?

 

[SDSmlf]

Zonie--I follow you, but please help me get my head straight.
Rather than making a bore cast or using an oversize ball rammed into the muzzle, are we saying that one could use a drill bit shank as a pin guage or a hard wood dowei turned to slip just so into the muzzle to determine land-to-land diameter. Having the land-to-land diameter we could subtract .010-0.20 for the proper ball diameter?

You will get ‘close’, but not close enough for what you want to do in my opinion. Standard drills in the .54” - .58” range are fractional in 1/64” increments. The closest you can measure is with a go no-go method. You will only be accurate to within .0156” (1/64”).

In your OP you stated you had an accurate load with double patched .020”linen, or .040”. If this is a compressed measurement, just increase your ball size .040” (you don’t mention the actual ball size you are using, or if you did, I missed that) and give that a try with your .020” patch (or get .040” thick patch material) if you don’t have the tools or experience to make an accurate bore measurement. In all honesty, doesn’t really matter what the actual bore size is if you have an accurate load. Puts you way ahead of the rest of the crowd.

Have an antique rifle with a bore size between 54 and 58 calibers and a coned muzzle.
Have been shooting a 54 caliber ball double patched with 0.020" linen. The load is accurate.
With 0.040" of patching on both sides of the ball, how would you calculate the approximate size of a proper fitted ball?

 

[Grenadier1758]

Thank you all for your insight and recommendations. Here's some additional data.

The .54 caliber ball I'm double patching with 0.020" linen has a diameter of 0.520 (Hornady). Yes, I could keep double patching since the accuracy is good but it is a pain-in-the-ass and uses up a lot of good linen.

Have some Cerrosafe casting metal on hand which could be used to cast an accurate slug of the bore. But the next question is, without removing the breech plug, what would be the best tooling to use to cast a slug from the muzzle and still be able to extract the slug from the bore. I was thinking something like a metal rod wrapped with friction tape to seal the grooves or would the brass rod trick work if I could seal off the bore with a wad of some kind while pouring Cerrosafe into the barrel.

Any help would be greatly appreciated

Since you got good accuracy using a 0.520" ball and two 0.020" thick linen patches, it would be worth the effort to try using a 0.535" ball and one 0.020" linen patch. You are going up 0.015" in ball diameter and dropping 0.020" in patch thickness. If the loading feels too loose, then a 0.025" canvas patch will probably be the next test.

 

[Rokon]

THANK YOU ONE AND ALL