Ball sizes

Newbie question.

Is there a rule of thumb for what size ball to use in any given calibre.

Welcome.
If you read enough posts around here, you'll see folks mention that every barrel is different, or words to that effect and each of us needs to work through the very wide selection of options for a load to identify the optimum performer for our needs.
That said, the 2 calibers I have the most experience with are 40 and 50.
For the 40, a .395 ball seems to be the most common choice among my fellow shooters but some like .390, and some like .400.
For the 50, most settle on a .490. That said...some like .495, or .500. In my most serious 50 caliber target rifle I shoot a very tight combination of a .500 ball and .018 (compressed measurement) patch.
Based upon a friend's experience...I can add that for the 32 caliber shooters, ball sizes seem to be all over the place. .310, .315, .320 all seem to have their fans. Ball size is just one of the variables that goes into building the best combination for a given rifle.
Hope this helps.

Most of the time .010 less then the gun size. A .50 shoots a .490 ball, a .54 shoots a .530 and so on.
It’s just a rule of thumb. A .75 shoots anywhere from a .690 to a .745.
Folks testing loads may try a .490,.495, .497 and .500 in a .50 rifle. Similar spreads are to be had with other calibers. I had a .54 that I shot a .526 in.
In general start .01 below. 99% of your shooting the performance difference between ball sizes won’t mater to your shooting. It’s the difference between a cloverleaf and one big hole.

We must have posted at the same time.

If you get some balls that are smaller than what you like (within reason), you can "shim them up" by using thicker patch material to make them snug in your barrel.

Bokbefok said:

Newbie question.
Is there a rule of thumb for what size ball to use in any given calibre.

Click to expand...

Yes I would say there is a rule of thumb for determining the ball size required by the firearm.

The rule would be to use a ball of sufficient diameter so that when you slug the bore with a patched ball then remove that ball to examine it. Look for the patch cloth weave marks deeply embossed into the ball surface where the patch was squeezed hard between the rifling lands and the ball surface.
Also you should see weave marks lightly embossed on the ball in the groove areas.

On my Lyman GPR 54 I tested a .530" ball with my chosen patch material. That ball size did not show cloth marks embossed all the way around the circumference of the ball. I even use a magnifying glass to examine the ball, there was no trace of the patch weave in the groove areas of the rifling.

Slugging the barrel with the .535" ball showed the weave marks all the way around the balls circumference.
I choose to use the larger .535" ball and test firing proved it to be the more accurate of the two sizes.

I can load the smaller ball much easier but I prefer the tighter shot grouping I get with the larger ball for fine target work and that is what the rifle gets used for 98% of the time.

I could have chosen to fiddle with patch thickness to make either ball work, but I choose to start with the patch material first. The 100% cotton cloth I choose was base on being not to thick and not to thin and had a very tight weave and was commonly stocked at the fabric store.
The patch cloth was double washed but not heat dried which would cause shrinkage (I could always go back and shrink in the dryer if the need arose) then ironed flat.

Even though I choose to use the larger ball I have happily noticed that when I need to unload the rifle without firing, the larger ball slides up the bore very easily. Much easier than when it when down the bore (clean). I suspect that the soft lead ball continues to distort while under pressure of the patch and rifling till a sort of equilibrium it reach.

Ball size and patch thickness are 2 common variables to experiment with, but there is also powder charge size, and type of powder to play with too. Some combo's shoot better with light charges, and some with heavier. And lubes make a difference too. For a load that is going to stay in the bore a long time (such as in hunting), you will not want a water-based lube (like saliva). Rust.

Another thing to fiddle with might be a buffer over the top of your powder charge, such as corn meal or cream of wheat. Yet one more might be a wad, such as wadded up toilet paper, a cardboard or felt wad, lubed or unlubed.

Lots of things to play around with in search of the "perfect" load.