Although the business end of many gun barrels seem to be a simple ‘pipe’, some medium size guns e.g. field guns, tanks guns etc and some small weapons have a widget at the end of the barrel. The design varies from a couple of horizontal holes to a number of slots.
I am curious to know the purpose of the widget, how it works and what determines whether it is fitted in a design.
Sound like the flash suppressor. Do you have a link with a pic?
could also be a muzzle brake.
Flsash suppressors are used to reduce the amount of muzzle flash when the gun is fired, however this is only noticeable if you are wearing night vision goggles.
A muzzle brake is used to disperse gasses behind the projectile to do one of two things:
1) reduce gas turbulence behind the projectile for a better trajectory
arrrgh hamsters cut my post short
2) a muzzle brake can also be used to reduce felt recoil by redirecting gasses as they exit the barrel
A friend and his buddy got new Armalite .50’s, the other guy didn’t install the muzzle brake correctly (ie., backwards). When he lit it off, it knocked him off the shooting bench. Needless to say, after correcting the problem, it was lot more fun to shoot.
It is one of the following:
A muzzle brake can reduce recoil felt by the shooter, but that’s not its purpose. The real purpose for a muzzle brake is to reduce the rise of the barrel due to recoil, so that you can keep the rifle (or pistol) on target during repeated firing. Not to keep your shoulder comfy.
Since the OP seemed to center around artillery and MBT guns, I would have to say that the diffinitive answer would be “muzzle brake” a.k.a. “gas brake.”
As to the other other suggestions (flash suppressor, sound suppressor, etc.), I fail to see how poking holes in them would help the intended function.
I call. I’ve never seen a brake threaded at both ends. Why would it be?
Ya got me, I thought they were threaded too. I speculate that maybe it has a set screw? that can be used on either end. Don’t laugh, I had a buddy who tried to put a muzzle brake on an SKS backwards…
A threaded barrel s one of the “evil” features under the 1994 crime bill. Semiautomatic rifles which can use a detachable magazine that can hold more than ten rounds are prohibited from having more than one of those features. The features are :
[ul]
[li]threaded barrel for attaching a flash hider or a flash hider[/li][li]pistol grip which protrudes conspicuously below the reciever[/li][li]attachment for firing rifle grenades (from the end of the barrel, not a separate grenade launcher)[/li][li]bayonet lug[/li][li]folding or collapsable buttstock. [/ul][/li] For a weapon with a pistol grip the only way to legally attach a muzzle break is with a non-threaded attachment or by permanently attching the muzzle brake to the threaded barrel by pinning or high temperature silver solder when the gun is manufactured.
Don’t forget, it could also be used for a flash hider.
There is another kind of ‘widget’ that’s actually used for sensing changes in the barrel. On the very end of a barrel on an M1A1 Abrams is a laser designator that measures the minute amount of droop or curl in the barrel from any environmental condition. This allows the gunner to make miniscule adjustments to his aim to get a precise hit on target.
Tripler
It’s not what you described in your OP, but it’s another kind of widget.
Prehaps I didn’t make clear is that the law is written so the flash hider and/or threaded barrel is considered one feature even when combined. This is important as only one feature is allowed. A threaded barrel counts no matter what attachment is on it - flash hider or muzzle brake. If the attachment is permant with pins, welding or solder the threads don’t count but the type of attachment does.
I won’t argue that the difference between a flash hider and a muzzle brake isn’t a fuzzy one at best but you are more than welcome to challenge the law and let me know how it goes.
Duh. Maybe BF didn’t explain it very well, but a threaded muzzle brake can be mounted upside-down, which would increase muzzle climb, rather than decrease it. Not exactly an increase in felt recoil, but very possibly less than pleasant.
One more minor clarification:
Flash suppressors don’t actually reduce the flash, they just redirect it away from the shooter’s line of sight, so that the aiming eye’s vision isn’t temporarily reduced by the flash. The actual muzzle flash is every bit as bright to an observer.
I’m done nagging now, I promise! 
Not to nitpick, but the gunner doesn’t make adjustments in his aiming. The computer does it for him. I’m an M1A1 tank crewman.
It’s called the Muzzle Reference Sensor, or MRS for short.
Thanks for all the responses.
Muzzle break / flash suppressor does seem to fit the widget that I have in mind.
Come to think of it, I do not recall seeing these devices on World War One guns, but they are quite common on WWII and more modern artillery. There again, they are not found on really large guns such as those of a battleship. What is the disadvantage of the device?
Padeye, I was just making a smartass comment on the clarity of your wording. Pay it no mind. Move along, nothing to see here …