Author Topic: The Silly Putty Effect  (Read 98 times)

Alan

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The Silly Putty Effect
« on: November 23, 2021, 08:17:11 AM »
I have always had an interest in Terminal Ballistics. This is the study of what happens when any given projectile hits its intended target. In this case, I’ll limit it to lead-based projectiles, without jackets, with an intended use as airgun ammo.

With this in mind, lead used in pellets and slugs, isn’t pure lead. Rather it is an alloy of lead, typically with some added tin (or antimony) to harden it up a bit. What specific alloy is used, depends on whether they’ll be cast or swaged, and obviously, their intended use. And, whatever the alloy, each and every one will exhibit a specific Modulus of Elasticity (ME). This describes any substance's resistance to being deformed when stress is applied to it. This includes the force applied to a projectile, when it reaches its intended target. It should be obvious then, that harder alloys have different MEs than soft ones. Let’s look at a material we’re all familiar with.

At some time in our life, we’ve all played with Silly Putty. It is a silicon polymer with some unique properties. One of those is what happens when you stretch it. Stretch is slowly, and it flows easily into strings. But pull it quickly, and the material snaps! Thus, an elastic limit of sorts is reached, wherein the material can’t stretch fast enough. In other words, when it reaches its ME, it breaks, rather than deforms. Since I’m not a metallurgist, I’ll call this the Silly Putty effect.

As mentioned above, any given alloy will act differently, under some given stress level. Whether is deforms or breaks up, has as many variables as a quantum theory equation! But sometimes, aside from scientific theory, an observation is worth noting. Digressing.

I have an FX Impact Mk II, and a Mk III. Both are shooting the NSA, 26.8 Gr. Slugs. The Mk II at ≈990 FPS, and the Mk III at ≈963 FPS. Subjective as it may be, shooting the two into a block of clay, a block of ballistic gel, a wet foam florist block, 2X4s, pigeons, you name it, the impact sound is quite different. And, when you examine the impact crater (if there is one), the nose of the ≈963 FPS slugs flatten out, while the nose of the ≈990 FPS ones, tend to break up into fragments. This is the “Silly Putty” scenario I’m speaking about!

As I’ve said, this is an observation, and not a scientific one. Nonetheless, it is an interesting scenario to think about.


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Alan

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