The Bullet Curve

You’ve heard of the bell curve?

It’s a common sight in any study of statistics (one of those words no one pronounces correctly). Almost every sort of group can be fitted into a bell curve.

So they say.

So if you had 100 people at random and listed, say, all their heights, most of them would be in the middle with the tallest and shortest on the ends. A plot of their heights (yet another word commonly mispronounced) should result in a bell shaped curve.

My Experiment

As you probably don’t know, one of my many interests is target shooting. It costs a lot to feed those guns, so I usually make my own bullets.

I look so serious and concerned when I should be having fun.

Anyway, I melt a bunch of lead (note the edge of the squirrel-cage fan at the lower right which makes for great ventilation) and pour it into moulds.

It makes two at a time. FYI, those grooves in the bullets will hold grease later on which will prevent leading of the gun barrel.

I drop the bullets from the mould onto a pile of towels because you don’t want to ding ‘em.

Even at today’s metal prices and the scarcity of free used wheel weights, it pays big time to cast your own.

At this point, the bullets are ready to be sized and lubricated (something I may talk about another time).

This time, however, I added an extra step before proceeding. I weighed each bullet.

Jennifer gave me an electronic scale last Christmas. Normally I use it to weigh out powder charges, but it occurred to me how easy it would be to weigh my bullets.

I made up a paper scale with the weight range of all the bullets. The particular bullet mould I was using theoretically drops a 240 grain bullet (there are 7000 grains in a pound, so these bullets weigh about 1/2 oz. each).

In reality, bullets rarely weigh exactly what the mould maker says. That’s because different lead alloys will be lighter or heavier than some “standard” lead. It’s not pure lead anyway, but usually has tin and other stuff mixed in.

My scale started at 246.5 grains and went up to 249 grains. I divided it every 0.1 grain.

As I weighed each bullet, I placed it above the paper scale. I simply stacked the bullets above each other when they had the same weight.

What do you think the final result was?

It’s not perfect, but I think it’s pretty dramatic proof of how ubiquitous the bell curve is.

The most common weight (tallest stack) was 247.7 grains. The vast majority fell between 247.0 and 248.5. Plenty good enough for my purposes.

And while the bell curve is common, it’s not common to find a group of objects that can be used to create their own “plot” of the curve.

Fun is where we find it, I reckon.