Shotgun choke question.

[CZ Shooter]

My knowledge of shotguns is pretty basic and I'm struggling with the "open choke" concept, which seems to be interchangable with "cylinder bore" as far as the terminology on the internet is concerned.
This is the common description, that could be found online in regards to this topic:

A shotgun barrel with Cylinder choke actually has no constriction at all. Its diameter is the same as the barrel’s internal dimension. This choke throws the widest pattern, so it is considered the most open choke. Cylinder is good for close shots on clay targets and game birds, and is also the most popular choice for those who keep a shotgun for self-defense and use buckshot.


This begs for 2 questions:

1) How can there be "no constriction at all" and how can the diameter of a foreign object inside a barrel be "same" as the barrels internal dimension?
This makes zero sense to me...if I insert an object inside a barrel....no matter how thin-walled this object, it still has to take away from the barrel's inner diameter?

2) Why stick something into a barrel and call it "open"...wouldn't the same thing be accomplished by simply not sticking anything at all in there?

Thank you in advance for any clarifications on this topic.

 

[rmsg0040]

Well if it has removable chokes, then the inside of the barrel is threaded.

The purpose of having removable chokes is to change the pattern to your desire.

Constriction is done at the end of the choke.

I shoot trap and have a fixed full barrel on one gun, on my other removable choke gun, I run full chokes.

 

[stubblejumper]

Actually , the chamber is larger than the bore, just as with any cartridge. That is why shooting a 3" shell in a 2-3/4" chamber can cause you problems. As for the choke, it can be changed to adjust the pattern size for different conditions, so it most definitely has a purpose.

 

[CZ Shooter]

Well if it has removable chokes, then the inside of the barrel is threaded.

The purpose of having removable chokes is to change the pattern to your desire.

Constriction is done at the end of the choke.

I shoot trap and have a fixed full barrel on one gun, on my other removable choke gun, I run full chokes.

Yes I do get the purpose of the chokes, but I don't understand why someone can stick a choke tube inside a barrel and still call it open?
I must be missing some key piece of information here.

For example I have an old 870 Rem Express and as far as I can tell, it is a wide open bore (cylinder bore?)...assuming it even accepts chokes, what would I gain by inserting this "open choke" for example?

 

[CZ Shooter]

Actually , the chamber is larger than the bore, just as with any cartridge. That is why shooting a 3" shell in a 2-3/4" chamber can cause you problems. As for the choke, it can be changed to adjust the pattern size for different conditions, so it most definitely has a purpose.

Yes I know that the chamber is larger than the bore, but I'm talking about the last 3 or so inches of the barrel.
Or are you saying that the barrel widens up before it ends again to accomodate the chokes?
Not sure if I understand your post correctly?

 

[Ashcroft]

As previously stated, choke refers to the amount of constriction at the muzzle of a shotgun barrel. Shotguns were (and are) developed to propel a loose mass of shot pellets, normally made of lead. Because this mass of pellets is not solid it acts as a fluid while travelling down the barrel and after leaving the muzzle. A straight tube from end to end with no muzzle constriction has no choke, which is indentified as "Cylinder" because it is a concentric cylinder from end to end and is the term for no choke. As you start to add muzzle constriction in increasing amounts (choke) the mass of the shot pellets becomes squeezed together tighter at the muzzle. They also stay more tightly clumped together as they fly through the air, spreading out more slowly than from an unchoked barrel. Think an adjustable nozzle on a garden hose or fire hose. The greater the muzzle constriction the greater the squeezing of this clump of pellets, to a limit. The goal of various amounts of constriction (choke) is to provide an ideal distribution of the pellets at a desired distance, too far spread apart and your target ( usually a bird) may not recieve enough pellets for a clean kill or may even slip through unscathed. Too tightly grouped together can result in misses on fast flying targets or mangled and inedible birds when hit. A shotgun is not designed nor intended to be a precise firearm like a rifle is, it is intended to hit small moving targets in rapid flight. Yes, they can be used to fire a single large projectile called a slug but these slugs all have some design feature that allows them to compress when encountering a choke constriction. This usually compromizes accuracy in varying degrees and is the reason that cylinder or no choke is preferred for slugs. The identifying names for the various choke constrictions evolved many decades ago, long before the arrival of screw in interchangeable choke tubes. It doesn't matter if the choke constriction is built into the muzzle of the barrel or if it screws into a barrel made for interchangeable chokes, the effect is the same, the choke designations (names) are the same. Don't forget, the threads in a choke tube barrel are cut into the interior surface of the tube, they do not protrude into the barrel so the transition from barrel bore to choke is as smooth as possible within production tolerances. For a visual reference and choke designations try going on site for one of the aftermarket choke manufacturers. It's a very large and somewhat imprecise field and you aren't the only one who is somewhat confused.

 

[rmsg0040]

Yes I do get the purpose of the chokes, but I don't understand why someone can stick a choke tube inside a barrel and still call it open?
I must be missing some key piece of information here.

For example I have an old 870 Rem Express and as far as I can tell, it is a wide open bore (cylinder bore?)...assuming it even accepts chokes, what would I gain by inserting this "open choke" for example?

I use to have a maverick 88, open choke, good fun with slugs

 

[REM3200]

If your gun has screw in chokes and your using a cylinder choke that choke is doing little more than protecting the threads from the shot passing through. When you change chokes you are tightening the pattern leaving the barrel to increase the effective distance of the shot pattern.. skeet, IC, LM, M, IM, Full.. there are other constrictions but those cover the range.

 

[CZ Shooter]

As previously stated, choke refers to the amount of constriction at the muzzle of a shotgun barrel. Shotguns were (and are) developed to propel a loose mass of shot pellets, normally made of lead. Because this mass of pellets is not solid it acts as a fluid while travelling down the barrel and after leaving the muzzle. A straight tube from end to end with no muzzle constriction has no choke, which is indentified as "Cylinder" because it is a concentric cylinder from end to end and is the term for no choke. As you start to add muzzle constriction in increasing amounts (choke) the mass of the shot pellets becomes squeezed together tighter at the muzzle. They also stay more tightly clumped together as they fly through the air, spreading out more slowly than from an unchoked barrel. Think an adjustable nozzle on a garden hose or fire hose. The greater the muzzle constriction the greater the squeezing of this clump of pellets, to a limit. The goal of various amounts of constriction (choke) is to provide an ideal distribution of the pellets at a desired distance, too far spread apart and your target ( usually a bird) may not recieve enough pellets for a clean kill or may even slip through unscathed. Too tightly grouped together can result in misses on fast flying targets or mangled and inedible birds when hit. A shotgun is not designed nor intended to be a precise firearm like a rifle is, it is intended to hit small moving targets in rapid flight. Yes, they can be used to fire a single large projectile called a slug but these slugs all have some design feature that allows them to compress when encountering a choke constriction. This usually compromizes accuracy in varying degrees and is the reason that cylinder or no choke is preferred for slugs. The identifying names for the various choke constrictions evolved many decades ago, long before the arrival of screw in interchangeable choke tubes. For a visual reference and choke designations try going on site for one of the aftermarket choke manufacturers. It's a very large and somewhat imprecise field and you aren't the only one who is somewhat confused.

Thank you.
I do understand the basic concept behind the chokes, but my issue lies elsewhere.
Let me ask this question from a different angle:

What would I gain by inserting an "open choke" to a cylinder bore shotgun?
In other words, what is the purpose of "open choke", as the words "open" and "choke" are mutually exclusive?

 

[CZ Shooter]

If your gun has screw in chokes and your using a cylinder choke that choke is doing little more than protecting the threads from the shot passing through. When you change chokes you are tightening the pattern leaving the barrel to increase the effective distance of the shot pattern.. skeet, IC, LM, M, IM, Full.. there are other constrictions but those cover the range.

Ok..so basically the sole purpose of the "open choke" is to protect the choke threads? (assuming of course that the barrel widens up to accomodate this choke so the inner diameter can remain the same).
If that is the case, that would actually go long way towards explaining this dillema for me...this could very well be the key missing information.

 

[stubblejumper]

Ok..so basically the sole purpose of the "open choke" is to protect the choke threads? (assuming of course that the barrel widens up to accomodate this choke so the inner diameter can remain the same).
If that is the case, that would actually go long way towards explaining this dillema for me...this could very well be the key missing information.

Of course the end of the barrel is oversize to accommodate choke tubes. if you look at many barrels, you will see that the last few inches of barrel is a larger outside diameter. The only other option is very thick barrels to allow for boring and threading them for chokes.

 

[Ashcroft]

I think your stumbling block here may be the confusion of the terms 'choke' and 'open' and ' cylinder'.
Choke is the overall term that refers to any constriction of the muzzle interior.
Open is an imprecise term sometimes used to describe lack of or no choke. It is not a recognized term for this purpose. If you chop six inches off a barrel it will have no (zero) choke left. It is sometimes improperly referred to as open or open choked but the real proper term for this barrel is cylinder bore.
Cylinder is the term for a degree of choke that is effectively no choke, no constriction. It is a measureable quantity and a recognized name as 'Full', 'Modified', etc are.
English is a strange language, especially since the Americans started influencing it.
J

 

[Falconflyer]

The end of the barrel where the choke tubes goes into is milled out to a larger diamter than the barrel bore. This allows a thin tube (choke tube) to be threaded into the milled out portion so that the inside diameter of the choke tube can be the same as the inside diameter of the barrel. Thus a cylinder bore choke tube which is actually not a choke (or constriction) at all.

 

[brybenn]

The end of the barrel of threaded for choke tubed barrels is larger to account for the threads. Using a cylinder choke tube gives you a cylinder bore pattern and the option of using other tubes of varying choke. You may use the same barrel for varying uses. I use a cylinder bore in my mossberg for skeet. A full choke for 27 yard trap. Mod for 16 yard trap. ###xfull for turkey and lm for waterfowl with steel shot. 1 barrel multi purpose. You will damage the threads by shooting it with out a choke in the barrel
A fixed cylinder barrel while useful is limited in its uses as the distance to target increases

 

[CZ Shooter]

I think your stumbling block here may be the confusion of the terms 'choke' and 'open' and ' cylinder'.
Choke is the overall term that refers to any constriction of the muzzle interior.
Open is an imprecise term sometimes used to describe lack of or no choke. It is not a recognized term for this purpose. If you chop six inches off a barrel it will have no (zero) choke left. It is sometimes improperly referred to as open or open choked but the real proper term for this barrel is cylinder bore.
Cylinder is the term for a degree of choke that is effectively no choke, no constriction. It is a measureable quantity and a recognized name as 'Full', 'Modified', etc are.
English is a strange language, especially since the Americans started influencing it.
J

Yes that is indeed it.
As someone who's not familiar with the proper terminology, I have no choice but to take things literally.

The term "open choke" is being thrown around very frequently even by the pros...and the fact that someone talking about having this "open choke" installed, while in the supporting pics (or video) I can clearly see a shiny metal choke inserted in the barrel....it is big time confusing.

The word "open" should deffinitelly not be used in connection with any choking device.

Thanks to all of you guys bringing some clarity into this topic for me.

 

[CZ Shooter]

The end of the barrel where the choke tubes goes into is milled out to a larger diamter than the barrel bore. This allows a thin tube (choke tube) to be threaded into the milled out portion so that the inside diameter of the choke tube can be the same as the inside diameter of the barrel. Thus a cylinder bore choke tube which is actually not a choke (or constriction) at all.

Yes the fact that the barrel widens up at the end was unknown to me before making this thread.
This brings me to a question about my 20 year old 870 Rem Express with 20in (I think) barrel.

I can't see any threads inside the smooth bore barrel and it seems to be the same diameter in and out.
I'm pretty sure it is a cylinder bore and I bought it brand new...it did not come with any chokes and I didn't think to ask.
Later on I bought a Norinco 870 clone called the Hp9 (I think)..same deal...cylinder bore, no chokes.

Does this mean that the two 870's in my posession are not meant to accept any chokes, or em I missing something?

 

[easy]

Does this mean that the two 870's in my posession are not meant to accept any chokes, or em I missing something?

Correct. Your barrels are not made to accept choke tubes because they don’t have a threaded area at the muzzle. Different barrels are sold with the threaded muzzle so they can accept choke tubes.
However, you can have your barrels threaded by a gunsmith to accept chokes.

 

[Ashcroft]

Yes that is indeed it.
As someone who's not familiar with the proper terminology, I have no choice but to take things literally.

The term "open choke" is being thrown around very frequently even by the pros...and the fact that someone talking about having this "open choke" installed, while in the supporting pics (or video) I can clearly see a shiny metal choke inserted in the barrel....it is big time confusing.

The word "open" should deffinitelly not be used in connection with any choking device.

Thanks to all of you guys bringing some clarity into this topic for me.

Hooray! See, I told you the subject of choke was a confusing and often misunderstood subject. Yes, the terms are frequently used incorrectly even by people that you would expect to know better but you know the old story........some people know a lot about a few subjects, some know a little about a lot of subjects, very few know a lot about a lot of subjects. Now you know more about choke than you ever knew before but in reality you are only scratching the surface of this subject.
It sounds like your two barrels are of the fixed choke variety ( not threaded for or equipped with removeable choke tubes) and probably Cylinder bore. These fixed choke barrels are usually marked near the breech end with the choke restriction (F, Mod, IC, Cyl, etc, or some in house code denoting constriction). Looking inside from the muzzle end the presence of choke can usually be clearly seen although the amount of choke can't be reliably determined this way. The only accurate way to determine the actual amount of choke is to measure the inside diameter of the choke at the tightest point using a bore gauge, then measure the inside of the barrel 5-6 inches in from the muzzle. Subtract the muzzle diameter from the bore diameter and the result is the actual amount of choke in thousandths of an inch ( or metric equivalent). You need to consult a choke table to put a designated name to this constriction but basically 0 difference shows no constriction, hence Cylinder choke, .020" or so of constriction on most tables would be Modified and .036" would show as Full on most tables as an example. You can get the rough inside measurements using an inside caliper but the old often quoted " if it won't pass a dime it's full choke" is useless because it doesn't measure the actual bore diameter and degree of choke is the difference between the bore diameter and the muzzle diameter. Surprise, all 12 guage guns don't have the same bore diameter. Think Browning with their overbore Invector and Invector Plus barrels, a dime will fall right through a modern Browning Full choke barrel and hardly touch the sides. Hell, a penny might fall through! And Browning isn't the only one with oversized bores.
Told you it was complicated and poorly understood.

 

[saskbooknut]

A choke tube bore is slightly larger in diameter than the barrel inner diameter, where it contacts the inner shoulder of the choke tube threaded recess.
Bad things happen to choke tubes if a projectile collides with or gets under the thin skirt of the choke tube. This is why you make sure your choke tubes are tightly threaded in.
A choke tube that has the same or slightly less exit diameter as the bore diameter is called cylinder. The origin of the term may go back as far as muzzle loading shotguns, which originally had no choke.

 

[BattleRife]

The word "open" should deffinitelly not be used in connection with any choking device.

I think that position is rather unreasonable. Describing a choke as "open" versus "tight" is a useful comparative term. Like referring to one sport bike as "fast" and another as "slow", you have to know it is used to speak relatively and imprecisely. If you want to be more specific you have to know the semi-quantified technical terms for degrees of choke (cylinder bore, skeet, improved cylinder, modified, improved modified, full, extra full), but if you are just chatting about shooting strategies with someone it is enough to mention using an open choke up close and a tight choke at longer range.

In fact even the technical choke terms are really just approximations, so that one shooter may think his modified is tighter than he expected, while another complains that his is too open.