Why do chokes work?

Londonshooter said:
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.
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Yes, that is what I think, and that may be the problem.


Ashcroft said:
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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The wad slows down in the barrel? It doesn’t accelerate continuously as the gasses burn behind it? So a shorter barrel shotgun has a higher muzzle velocity than a standard barrel? That doesn’t seem right.


Are you guys sure the shot and shot cup separate and string out in the barrel? I can find plenty of great videos of pistol and rifle bullets leaving the barrel, but there’s precious little depicting a shotgun muzzle in super duper slo mo.

This gif was the best I found.

wateryshockingcolt.gif



It’s a crappy gif, but it looks like the shot leaves the barrel in one big clump.


Edit: aaaand of course the gif isn’t giffing.
 
kodiakjack said:
Yes, that is what I think, and that may be the problem.





The wad slows down in the barrel? It doesn’t accelerate continuously as the gasses burn behind it? So a shorter barrel shotgun has a higher muzzle velocity than a standard barrel? That doesn’t seem right.


Are you guys sure the shot and shot cup separate and string out in the barrel? I can find plenty of great videos of pistol and rifle bullets leaving the barrel, but there’s precious little depicting a shotgun muzzle in super duper slo mo.

This gif was the best I found.

wateryshockingcolt.gif



It’s a crappy gif, but it looks like the shot leaves the barrel in one big clump.


Edit: aaaand of course the gif isn’t giffing.
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Anything beyond 24" is just for pointability/swing/sight radius. After 24" your shot is not longer accelerating. Baring hand loading hot loads.
 
Londonshooter said:
Yeah, I gave a reference that countered my own argument.
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That’s noble. Respect. :cheers:

But where does that leave me with my inquiry? It still seems as though any restriction at the end of the barrel would cause the deflection of the shot, which would otherwise be traveling in a perfectly linear direction.
 
kodiakjack said:
That’s noble. Respect. :cheers:

But where does that leave me with my inquiry? It still seems as though any restriction at the end of the barrel would cause the deflection of the shot, which would otherwise be traveling in a perfectly linear direction.
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Your assumption that the shot is all happily travelling together in a linear fashion is misguided. Under rapid acceleration, the shot is "jostling" down the barrel, and being compressed radially and axially against the wad. Meanwhile, the barrel itself is subject to vibration and recoil induced motion. Even in a vacuum and no choke, these factors (and particularly the radial compression) would cause the shot to splay upon exiting the barrel.
 
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I think the OP has a refreshingly analytical mind and has asked a very good question. The variety of different answers that have been given clearly demonstrate that many of us (including me) do not actually understand the physics that goes on with barrel constriction.
 
ninepointer said:
I think the OP has a refreshingly analytical mind and has asked a very good question. The variety of different answers that have been given clearly demonstrate that many of us (including me) do not actually understand the physics that goes on with barrel constriction.
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Hah. I’m not sure my wife finds it “refreshing” anymore :p

Thanks.
 
Juster said:
f74d2547af-Shotgundata-Sequence_1500.jpg


Here the choke compresses the wad, how that reduces spread, I'm not sure.
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Great pic! Exactly what I was looking for as a video. I’d love to see the same type of photo taken with different chokes though. Especially the extreme spread, like a turkey choke vs cylinder bore.

Looking at this pic... I’m thinking... maaaaybe the only thing a choke accomplishes is to sort of “crimp” the shotcup as it exits the muzzle, so that it delays opening up in the on-rushing air. The cylinder bore perhaps opens up in the first inch after leaving the barrel, whereas with the unknown choke above, we can see it flies a few feet before starting to open. Perhaps all shot spreads out at the same angle from where the shot cup opens up, and the choke’s function is simply to carry the shot closer to the target before opening up and starting the expanding spread process.

That’s how the federal “flight control” buckshot works too right? The shot cup is designed to stick around twice as long before releasing the buckshot... hmmm.
 
Don't get too focused on that plastic wad. Choke works and works well on cushion wad loads without any petals - there may be a few more flyer shot from barrel scrub, but patterns are excellent at the pattern board with old fashioned stack wad loads.
 
A choke is nothing more than a restriction/decrease in bore/barrel diameter. That decrease in diameter is not instantaneous, it begins a few centimeters before. This results in a cone. The cone induces a trajectory change for any pellet not precisely traveling in the middle of the bore. The goal of the choke is to bias most pellet trajectories towards the midline of your shotpattern . A cylinder choke or no choke would have most trajectories prrallel to the midline of your shotpattern. Once the shot has exited the bore, external forces begin to disperse your pellets. The tighter choke induces a larger change in trajectory hence tighter patterns. The shotcup/wads function is to reduce deformation of the spherical pellets. Undeformed spheres are aerodynamically superior and are less influened by the air as they travel. Steel shot is harder than lead, generally requires less choke for the same pattern.
 
Your thinking that barrels are perfect cylinders is flawed. Most barrels have forcing cones. Different wads and chokes have different effects. Ive had to pull lead out of a friend while using a ported choke. The shot was not contained in the plastic cup. Also as mentioned earlier explain leading in barrels if its contained in plastic. Same with steel shot scaring barrels.
Choke is a constriction. Any constriction effects shot patterns. Generally tighter the choke the tighter the pattern however there is a point where it reverses but thats with specialty chokes for card cutting and such. Even shot size and speed effect patterns
I also shoot scatterguns without using shotcups chokes still work. Even when using black powder. Its a complex matrix of acting forces

Also. How could you fire a gun in a vaccum? There wouldnt be any combustion
 
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