Why do chokes work?

kodiakjack

kodiakjack

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Ok. Stupid question time. Bear with me...

I know THAT shotgun chokes work, but I’m fuzzy on WHY shotgun chokes work.

Hear me out:

Let’s say you set up a little gun range in a complete atmospheric vacuum. You fire a cylinder bore shotgun at a target. The pattern spread would just be a single hole in the target as though the shot were a slug. This of course is due to Newton’s first law “An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an outside force.” The shot cup and shot are all travelling the excact same direction down the barrel, and leave the uniformly shaped barrel at the muzzle and carry on towards the target without opening up or discarding the shot cup, because there’s no air to force its way into the shot and push everything apart.

Now imagine you take another shot in this vacuum chamber with a full choked shotgun. The shot and cup travel down the barrel as they did in the first scenario, but as they leave the barrel, they hit the choke, causing the shot and cup to compress. This would act as the “outside force” Newton mentioned. This impact with the choke would jostle the shot around and against each other, causing it to depart from the straight, linear path it had been on, and instead causing an erratic flight path resulting in a slightly wider pattern (or at least a larger hole) in the target.

Now if we let the air back into our chamber and try these shots again, allowing the dense air to open the shot cups and spread out the pellets, why is the full choke printing a tighter pattern? Why doesn’t it deflect and disrupt the shot just a tiny bit more than the cylinder bore like it did in the vacuum? I can make sense of it if there was some big device several feet after[\b] it left the barrel that redirected the already expanding shot cloud into a more linear path... but the full choke isn’t doing that. It’s just deflecting the the filled shot cup that was already sliding happily along in a nice linear path.

So what gives? Anybody got a 25 yard long vacuum chamber I can go play in?
 
It is like the water nozzle- the full choke compresses the shot string and lengthens it which produces a narrower pattern. The choke acts like a focusing element. A similar effect can be found with optics when people talk about a beam "waist" where a collimator is used to manipulate a laser. The laser is typically focused to a certain distance to get better long range density. The focusing element works the same way as the choke.

The vacuum analogy is correct- however when real world diffusion effects are added, the benefit of starting out wide and focusing to narrow will make a denser down range pattern than starting perfectly collimated and letting the diffusion happen.
 
Juster said:
One possible cause would be slowing down the wad and exposing the lead to less blast. Or the water hose analogy, the shot flows as a liquid.
Click to expand...


Could you expand on this a little bit? By “blast” do you mean muzzle blast? Or the initial blast of onrushing air as it leaves the muzzle?
 
Thanks for indulging me :p


cartwheel said:
It is like the water nozzle- the full choke compresses the shot string and lengthens it which produces a narrower pattern. The choke acts like a focusing element.
Click to expand...

Except that, as it passes through the choke, there IS no “shot string” yet right? I mean, it would make a little more sense to me if there was a loose string of shot traveling down the barrel all spaced out, then the choke acted like a nozzle focusing it... but when the shot goes through the choke, there’s no “string” yet. Just a bunch of very tightly packed shot held securely against the back of the shot cup by the acceleration. It doesn’t string out until it’s a few yards down range, right? That’s my understanding anyway.




A similar effect can be found with optics when people talk about a beam "waist" where a collimator is used to manipulate a laser. The laser is typically focused to a certain distance to get better long range density. The focusing element works the same way as the choke.
Click to expand...

I think I see what you’re saying here, but I’m reluctant to think of it in terms of light and lasers, because (aside from gravity) they would act the same was as the shot in the vacuum chamber. (No deflection or deceleration due to air resistance.) Also, light can pass through itself, unlike lead packed tightly into a shot cup.

Past the beam waist, the beam gets endlessly wider. And with shot, if we set up a thin paper target every few feet out to 20 yards or whatever, I’m pretty sure we don’t see a “beam waist” in the pattern, do we?

The vacuum analogy is correct- however when real world diffusion effects are added, the benefit of starting out wide and focusing to narrow will make a denser down range pattern than starting perfectly collimated and letting the diffusion happen.
Click to expand...

Yeah... I mean, like I said: I know chokes work. There’s no denying that. But it just doesn’t seem like what happens should happen.
 
I got a headache reading the question and a second one from the answers. In Layman's terms the wad is putting pressure on the shot column forcing it to expand, If the barrel were long enough you would get full choke patterns from a cylinder bore because the shot would out run the wad. The same effect is achieved by having choke constriction retard the wad allowing the shot column to out run the wad. The good old "KISS" principle at work!
 
I guess the confusion is because you think the shot is encased with plastic at the muzzle, or am I not reading that correctly(?) The bulk of the shot column is already ahead of the wad/shotcup when it reaches the choke.
 
In the first place your assumption of how the pattern would not change in a vacuum is incorrect. There are some other forces acting here that you have forgotten about.
1. The wad is being retarded by friction with the barrel wall. As it slows, more and more pellets have room to move away from centre.
2. The pellets on the bottom ( closest to the powder) are under pressure from the explosion to push against the pellets ahead.
3. The pellets are compressed together travelling through the barrel and will randomly spring apart when released from constriction.
Of course, we don't operate in a vacuum and chokes are designed to work in the real world where air resistance on wad and pellets, out of balance pellets, deformed pellets, muzzle blast, gravity, wind and magic all affect the shot string. The evolution af choke boring is fascinating and took place gradually and intermittently over 50 years or more brfore it was finally generally understood well enough to be applied consistently and repeatably in the mid 1870's.
 
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