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Large ball+thin patch vs small ball+thick patch

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CoyoteJoe

70 Cal.
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While putzing around the shop I picked up a 6" section cut from a GreenMountain .50 caliber barrel. What could I do with this? Well one thing I could do was to push some balls through it and see how they came out.
First I pushed a .530" Speer ball through to get a good measurement of the bore. It took heavy blows of a rawhide mallet to get that bare ball started but once down 1/2" it pushed very easily on through. I take it this was because pure lead is pretty much non-elastic so once formed to the bore there is very little friction in pushing it on down. I miked the slug at .500" land to land and .520" groove to groove.
Next I tried a .500" cast lead ball in .018" pillow ticking patch lubed with mutton tallow. The combined ball diameter and two thickness of patch totaled .536". Again I could not start the ball with a bare hand but had to resort to the mallet. Once started by mallet I could push it on through with hand pressure on the knob of the ball starter. The .500" ball showed distinct cloth weave pattern corresponding to the lands of the GM barrel.
Last was a .490" Hornady ball with a patch of .026" cotton canvas, mutton tallow lube. Combined total of patch and ball equals .546". This I could start by rapping the starter with the heel of my hand but I probably would not want to do that all day. Once started I could not just push it on through but had to keep striking the starter with my hand to drive it down. The fabric imprint of lands into the ball was not nearly so visible as it had been with the .500" ball, even though the total of patch and ball was .010" greater.
First ball on the left is the .530 bare ball showing bore contact of both lands and grooves. Next, in the center is the .500" ball and .018" patch. Last, on the right, is the .490" ball and .026" patch.
balls2.jpg

Imprint of the lands on the .490" ball were very light and hard to see, even though the combined ball and patch measured .546". The imprint of lands on the .500" ball was more distinct. Of course the .530" bare ball showed bore contact of both lands and grooves and fins of lead draw out by the lands.
 
I would be interested in what the accuracy results would be with a greatly undersized ball and a very thick patch. I suspect as long as it loads tight, the ball still has to spin once it leaves the muzzle the accuracy would be good, but have never tried it.
 
ive done some testing with my pedersoli 50 cal long rifle. i used a .490 ball and a .495 ball which patches of various thickness. in the end i found the .490 ball with a thicker patch to hold better groups then the larger ball with a thinner patch.

having a smaller ball and thicker patch has another advantage aswell. heavier powder charges are less likely to burn threw the thicker patch.

-matt
 
My GPR 50 was shooting pretty well with a 490 and .018 ticking but I loaded without powder and unloaded it with my unloader. The recovered ball looked as though a larger ball might help. I have some 495's to try when it warms up a little.

This was a very informative post Thank You! Geo. T.
 
When I figure what RB dia. and what patch thickness to use, this is how I do it....

First off the groove dia of the bore has to be obtained....on my .54 that would be .540 + 2 groove depths {.015/side} for a total of .030 which equal a groove dia of .570.

Using a .530 RB w/ an .018 patch = .566 {not enough to obturate the groove dia.}
.530 w/ a .020 patch = .570 {barely enough}
.530 w/ a .022 patch = .574 {should obturate the groove dia.}

Using a .535 RB w/ an .018 patch = .571 {barely enough}
.535 w/ a .020 patch = .575 {should obturate the groove dia.}
.535 w/ a .022 patch = .579 { should obturate the groove dia.}

Because of easier loading for the 2nd shot while hunting, I use the .535 RB w/ a .020 patch and the accuracy is fine. The powder charge is 120 grs 3f.

Also whether any of these combinations actually obturate the groove dia. is for another discussion...but at least filling the groove w/ patch mat'l is an attempt.

This is probably info that most know, but perhaps some aren't aware of.....Fred
 
I'm in the middle of experimenting with a thinner patch. What are your thoughts on a 7 grooved barrel where a groove is directly opposite of a land?

My grooves are .016 for my .45 barrel. I'm using a .020 patch with a .440 ball that takes about 3 hard smacks to get it pass the crown, and then it takes all my body weight to push it down the half way point of the barrel where it gets easier.

That ball and patch combo measures out to .480. Two grooves plus the land diameter equals .482. You wouldn't think it would take a pounding to get it started, but it does. It stresses the fibers of the patch where the lands contact it.

That's why I'm wondering if for an odd number of lands to grooves where the groove is directly opposite a land, you should take the dimension of the land to the groove as the consideration for patch choice, which in this case is .466.

I'm going out to find some .015 material today to experiment for future range sessions.
 
Testing is the only answer. I don't believe one can take a purely mathematical approach to finding accuracy. Careful measurement and calculation can give you a reasonable starting point but from there it is cut and try. Two identical barrels from the same maker may require very different combinations for best accuracy but only testing will tell. As a general rule of thumb I think shallow grooves, say .005"-.007" will do best with a ball nearer bore size, or even over bore size, and a thinner patch, say .015"-.018". A barrel with deeper grooves, .010" or more, may be better with a thicker patch, .020"-.030"+ and that thick patch will necessitate a smaller ball to still be loadable. But again, that's just a starting point, you need to experiment from there. Do a lot of shooting and keep good records and over time you will begin to see "trends" but also exceptions.
 
Testing is the only answer. I don't believe one can take a purely mathematical approach to finding accuracy.

Halleuiah! Finally, after lots and lots of words, some wisdom.
Try it, if it works stop talking and start shooting. Overbore size balls can be used to achieve excellent accuracy. I have seen it and have tried it. Thin patches are sometimes needed with shallow groove barrels.
Time spent at the bench burning powder is where your answers will be found.
 
This kind of sounds like my Traditions barrel. At the muzzle, a .490 lead ball over a .020 patch is difficult to start, but a few inches down, it pushes quite easily, and a few inches from the breech, it seems to tighten up again. This happens both from a clean state and after shooting. It is more noticeable after a shot though. :doh:
 
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