Crowning For Round Ball, Plain Bases And Minies

[nkbj]

I'm fixing to put some finishing touches on a little Spanish half stock to handle .375 and .380 round ball and will hopefully work well with all three (ball, plain bases and minies).
What have yall seen in so far as the effects the types of crowns on barrels have had on your accuracy with round ball, plain bases and/or hollow bases?

 

[Zonie]

What I've seen is often, the sharp edges where the crown meets the rifling grooves and the bore are sharp.

Often these sharp edges will cut the patch when patched roundballs are loaded.
Because of this, I always dull up all of the sharp corners on all of the barrels on my muzzleloaders by using a small, 1" X 1" piece of 180 grit silicone carbide (black) wet/dry sandpaper and my thumb to force the sandpaper down into the muzzle.

I then rotate my hand back and forth, letting the shape of the crown centralize it.
By the time I'm thru. there are no sharp edges and the crown has a highly polished look to it. If I don't like the bare metal look it has, I use some Birchwood Casey cold bluing to darken it.

 

[nkbj]

Over the years I've used round and conical grind rocks (the ones with the 1/4" spindle) to do the initial shaping (have a bag of those) and done the emery paper / thumb rounding you're speaking of there. Started trying out the emery paper rounding on this small bore a little bit last night and after using thumb pressure for a while began to think about how a tool could be rigged up to use the paper and a drill. Still cogitating on that one.
About the shape I want to end up with, I'm almost convinced that a 45 degree angle could be a nice goal to work towards. As-received the muzzle has a greater than groove depth chamfer on it so perhaps I will just smooth out what currently exists and see how she do. After all, you can take more off but not put it back (and getting back to a square and flat end of the barrel to start over isn't fun).

 

[bang]

I like a multi faceted carbide ball file. Turn by hand reverse. Nice because even in reverse it still cuts but very lightly and doesn't wear.

 

[nkbj]

No larger than the groove diameter is, perhaps a wooden dowel can be turned to shape and end split to hold emery paper. Or, sometimes tape will hold the paper with the paper shaped and wrapped around the end.
This working in miniature can be worrisome.

 

[nkbj]

Searching high and low, finding nary a 45 degree grind rock.
Time to make up a tool.

 

[bang]

Searching high and low, finding nary a 45 degree grind rock.
Time to make up a tool.

I have cut emory cloth so it fits on a round surface without overlaps then glued it to the round end of a round shank screwdriver and turn it slow with oil to polish existing crowns.
The multi faceted carbide ball file hand turned reverse out to even to groove I use to make crown. Main thing crowned or not is the muzzle must be square to bore and the lands and grooves free of burrs and smooth.
Crowning mainly protects from incidental damage emproaching to the bore edge. Side advantage of beveling lands to grooves is easing PRB start and reducing patch tearing. So as long as muzzle is square to bore and clean it should shoot proper.
If I was to choose a tool for, lets say, a 50cal, I would consider 5/8 maybe 3/4 round. I would not use a rock because a rock wears and can change desired design. Another is a hard steel round head bolt and lapping compound. Takes a bit more time and more clean up but will make it smooth and even.
Advantage of ball file is you don't have as much concern to hold alignment to bore. Advantage of by hand is lighter touch provides more control but bit more time. Turning reverse, no biting.

 

[hanshi]

It's easy to overthink this crowning process. Really all that is needed is polishing a smooth transition from the crown on down into the lands, maybe 1/8".

 

[nkbj]

Right now I've been cogitating on how to do that to a .38 bore that currently has a bevel on it that needs to be trued up and polished. Haven't contrived an object yet to do it with. All my angle rocks have angles that are gonna reach down the bore more than a 45 degree would. And the existing bevel will not let me just thumb press emery paper on the cut surface. The hole is too small. So I'm still looking for the way to do this once.

What I might end up doing is multiple stages. First take a little off with a rock I have, polishing down bore with emery paper on the angle rock. Then dealing with the area closer to the flat end of the muzzle. Though this is primarily going to be a ball gun but intending to have it perform well with hollow base and plain base bullets as well, the little bitty crown is important.

 

[Greasecookie]

Valve lapping compound on a proper sized brass round head screw, turned in a drill motor, works well also.

 

[nkbj]

Thank you for all the ideas.

That small diameter is thwarting the thumb method with that previously cut bevel.
Gonna look at the screw heads.
And there's often something unbeknownst in a drawer at the hardware store (this being camper and farming country).

 

[nkbj]

McMaster-Carr has the 90 degree rocks.
Yippee!