Picking a patch and ball size based off of slugging the barrel

[Onemancoyote]

A friend has me working on an under hammer pistol of his. He has never shot it. After slugging the barrel the grooves measure .460" and the lands measure .445". How would I go about picking a ball diameter and patch thickness to start testing with?

 

[Eric Krewson]

I don't know for sure but I would start with a .440 ball and a patch around .015 or .018 or even .020.

 

[wiscoaster]

(ball + (patch * 2) <= grooves) && (ball < lands) := first patch size.

 

[Onemancoyote]

(ball + (patch * 2) <= grooves) && (ball < lands) := first patch size.

So... (.440 + (.008 x 2) = .456.

a .440 ball and a .008 patch?

Is it (ball + (patch * 2) </= grooves)? Meaning it should be less than or equal to groove?

 

[Banjoman]

Just to start, a .440 ball and 100% cotton patch made from old sheet or pillow case or tee shirt. Lube of your choice.

 

[wiscoaster]

(ball + (patch * 2) <= grooves) && (ball < lands) := first patch size.

So... (.440 + (.008 x 2) = .456.

a .440 ball and a .008 patch?

Is it (ball + (patch * 2) </= grooves)? Meaning it should be less than or equal to groove?

Take it with a grain of salt; I just made it up this morning loosely based on experience, and I guess intended to recommend 0.010 or thinner as first trial patch thickness:

(0.440) + (0.010 * 2 ) = 0.460

Theoretically 0.010 should be enough to squeeze that patch material down into the grooves to catch the rifling, but at the same time it might be too thick for the lands.

I'd be curious to know how it works out. Much of the time trial and error wins over science and math.

 

[Grenadier1758]

I tend to start with a ball 0.010" smaller in diameter than the land-to-land diameter. In this case, a 0.435" ball would require a custom mold. I would start with the 0.440" ball. The groove depth is 0.0075. To get a good seal, the patch needs to compress to 0.010" (0.0025" for windage between ball and land + 0.0075" for depth of groove). Most tickings of 0.015" published thickness will compress to 0.010". You will need a tight weave of sturdy cloth to withstand the fitting into that windage space by engraving into the ball or further compression. On a new barrel, there will be cutting of such patches. Avoid prelubed patches as the prelubed patches often deteriorate in storage and fail as a patch for such a tight fit. You will need a short starter to get that ball and patch to load.

 

[wiscoaster]

I tend to start with a ball 0.010" smaller in diameter than the land-to-land diameter. In this case, a 0.435" ball would require a custom mold. I would start with the 0.440" ball. The groove depth is 0.0075. To get a good seal, the patch needs to compress to 0.010" (0.0025" for windage between ball and land + 0.0075" for depth of groove). Most tickings of 0.015" published thickness will compress to 0.010". ......

Thanks!! Good knowledge for me to learn. I had considered fiber compression, but didn't know how to account for it. Maybe I'll come up with a new formula based on that new information. Science and math learns from trial and error experience!!