How does load compression affect shooting?

In looking at muzzleloader web pages, mailing lists and advice columns over the years, I have seen inconsistent information about just how much 'squish' one should put on a load. The answers are always 'consistent', which is understandable, but the actual amount is often decribed as 'firm', 'hard', 'just seated', and so on. Watching actual shooters at the range, I have seen everything from gentle pushes through 'whanging' the load with the ramrod or driving it home with a mallet. So I said to myself - this sounds like an interesting experiment! Just what, if any, is the 'right' amount of compression to put on a black powder load, and what aspects of performance are affected?

Setting Up

Patch clamp In setting this up, it immediately became apparent that I had to be careful and separate compressing just the powder versus the powder and patched ball combination. 'Whanging' a ball on top of a powder charge certainly compresses the powder, but it also 'obturates' the ball, expanding it into the rifling. This may or may not be a bad thing, but I wanted to separate the two effects. I machined a flat-bottomed ramrod tip which just fit the bore, so that I could just compress the powder before loading the patched ball. I also modified my regular ramrod tip so it just matched the curve of the ball in order to minimize any distortions from pressing on it.

For the tests, I used my Pedersoli .45 caliber flintlock with a 30 grain charge of Swiss 3F, which is my usual load. This may sound like a light load, but it is an excellent one for target shooting; if the load goes over about 35 grains, the rifle becomes much more hold-sensitive when shot off the bench, with pronounced vertical stringing. I also used a Hornady swaged .443 round ball with a dry-lubricated .010" patch and a touch of Lehigh Valley patch lube just before loading; which keeps the fouling to a minimum. The bore was wiped and dried between the strings of five shots each.

Since compression is hard enough to judge, I decided to test only four variations:

Before anyone goes nuts about the 'Loose' variation, let me point out that it is perfectly safe to have a small space between the powder and ball. In fact, this is the way almost all modern cartridges (and many old ones) are loaded. To 'standardize' the compression, I used the simple expedient of standing the rifle vertically on a firm surface and dropping the fiberglass ramrod repeatedly until it bounced at least three times (it also makes a peculiar 'poing' sound when no more compression can be achieved). In the 'Compressed' charge, the powder column could only be reduced by the equivalent of about 5 grains of powder; Swiss is a very hard powder, and others may be different. All shots were from a bench at 50 yards, using the original open sights on the rifle. Considering my vision, I consider I can hold about +/- 1/2" horizontally and +/- 1" vertically at best. The table below shows my results for average muzzle velocity, standard deviation of MV, group extreme spread and group position relative to the bullseye.


Condition Loose Normal Compressed Whanged
Average MV 1266 1304 1347 1378
Std.Dev.MV 3 19 12 9
Group (ES) ?? 3.5 3 2
Position ?? Up 1 0-0 Up .5


Using the same powder charge, the muzzle velocity changes by over 100 fps, depending upon the packing of the ball and charge. If we campare the MV at the normal compression and the 'whanged', it translates to a difference in drop of about 1/2" at 100 yards - unnoticeable to me, but maybe not to a good target shooter. The deviations in MV varied a bit, but all were within acceptable limits. Most interestingly, the 'Loose' packing gave the lowest MV deviation of all, but I guess that makes sense, because that would be the most consistent condition, even if it's not the best one. The accuracy, however, was awful; two shots didn't even make the paper, and the three that did had a spread of 9". At least one reason was that the patches were blown to varying degrees; one had the entire center removed. Normally, my patches show little wear, so this was a puzzle. I theorize that when the rifle is shot with its usual firm ball and patch seating, the initial accelleration comes from the unburned powder at the base of the ball shoving against it and acting as a kind of gas seal. With the powder loose, the hot gasses can directly reach the base of the ball.

I have heard people speak for and against the procedure of 'whanging', or bouncing the ramrod, but it gave the best results here. If this is done, I think having a good match between the ramrod tip and the ball would be a good idea so that ball distortion is minimized. I don't think some defacing of the top of the ball is important; many tests have shown that shooting a round ball with the sprue up is no less accurate than shooting a ball without a sprue. I recall, but can't find a reference to a special loading rod called a Kadoody, which was essentially a slide-hammer and would have the same effect as a 'whanged' ramrod, but possible more reproduceable. There is at least one advantage of 'whanging', the ball is expanded to fit the bore at loading, so you can use a relatively loose patch-ball combination, which greatly eases loading. I really like this benefit, and I can't get more ball deformation than someone hammering a tightly fitted ball down a dirty barrel...

I will be testing other powders in the future, including 'black powder substitutes'.