Hypothetical barrel length question

[ultralightbackpacker]

22LR rifle barrel. Generally speaking the longer the barrel the more accurate and perhaps the faster velocity right? I guess the reason is the gas gets to build up more pressure etc.

Anyway,

Question#1 How long of a barrel is considered to long? Could one have a 4 foot barrel and it would help with velocity?

Question #2 How long of a barrel before it loses velocity from friction of rifling?

Question #3 How long of a barrel before the projectile never even clears the barrel because it's just to long?

Yeah I'm pretty bored today.

 

[steveno]

I don't think you gain much with a barrel length over 20 inches long in a 22 long rifle

 

[Duke of Doubt]

These are pretty fun questions.

Most of the accuracy gains from longer barrels come from increased sight radia index -- the distance between the front and rear sights. You can hold the gun steadier when visible wobble is more apparent via the front sight.

Some of the accuracy gains come from the additional barrel weight hanging on the front of the gun -- it keeps the front from wobbling so much.

Some of the accuracy gains do indeed come from additional muzzle velocity based on complete combustion of powder and greater pressures in longer barrels.

Friction would depend on the bullet shape and the bullet jacketing as well as the barrel rifling -- how many grooves, how deep, how wide, how cut. That friction would then determine how long the barrel would have to be before the bullet loses velocity inside, and eventually stops. I really don't know, but I'd guess that for a .22, cheap plated round in a Marlin microgroove barrel, the thing would have to be much longer than four feet. Maybe a hundred feet, who knows?

 

[Dr. Tad Hussein Winslow]

I have heard it alleged many times (and accepted as conventional wisdom) that with subsonic and standard velocity ammo, that somewhere between 12" and 14" of barrel length, the force exerted by friction of the bullet against the bore exceeds the force of the remaining expanding gases pushing against the bullet, so that the bullet begins slowing down rather than speeding up from that point forward. I've also heard that with Hi-Vel ammo (which anymore, hi-vel IS the new standard vel that most people use), you can see gains well past 12-14", even to the point of getting gains going from 20 to 24". Never tested it myself. I once chrono'ed some Aguila Super Vel ammo which claims over 1700 fps from a rifle, and from a 5" .22 pistol, I got 1325-1350 fps, so they weren't lyin!

Question #3 How long of a barrel before the projectile never even clears the barrel because it's just to long?

That's a good question and I don't know, but it's probably gonna be in the 6-10 foot (72-120") range or more for a .22 Hi-Vel that peaks out at around 1250 fps, I would guesstimate. It's gonna depend in part upon the bullet length & shape and therefore how much contact is being made with the bore surface, leading to increased friction.

 

[rcmodel]

16" - 18" actually.

At any rate, a .22LR is not going to gain any velocity at all over 24" - 26", and much longer then that it would start slowing down.

There is something to be said for a shorter stiffer barrel being more accurate then a longer less stiff one too.

As for how long a barrel would have to be before the bullet would get stuck?

I don't know about .22LR, but .22 CB caps run out of steam & can get stuck in barrels longer then 24".

rc

 

[Macmac]

There is no way to know how long a barrel would have to be before the bullet wouldn't come out. A squib load in a pistol can have that happen and it does when re-loads are not cared for in the making very well.

I might imagine a barrel 1/2 mile long might still clear a 22 loaded right. I might guess a barrel 1/2 mile long would create friction to slow the bullet too.

 

[eye5600]

Not 22lr, but interesting on barrel length:
http://accurateshooter.wordpress.com/2009/02/05/barrel-length-and-velocity-barrel-cut-down-tests/

 

[rcmodel]

I can assure you no bullet out of any caliber sporting arm is going to make it in a half-mile long barrel!

As soon as the expanding powder gas fills the available bore volume, bore friction would start slowing down the bullet immediately.

And as the hot gas cools quickly inside the bore, it would condense, and might even stop the bullet and suck it backward at some point if the vacuum got to be high enough.

rc

 

[HGUNHNTR]

A longer bbl does not aid in mechanical accuracy. The bullet does not know how long the bbl was it shot out of. Accuracy, as stated before, is greater with a long bbl only when using open sights. This helps increase the accuracy of the SHOOTER, not the bbl or the firearm.

As for velocity, as soon as all of the powder is burned, no more pressure is devoloped. If you have a 4 foot bbl for a .22LR, you will fing that the friction of a bbl that long will SLOW the bullet down. Why do standard caliber rifles have a shorter bbl than Magnum calibers....less powder to burn. There is no increase in velocity if there is no more powder left to generate more pressure.

 

[Mello]

Check out www.ballisticsbytheinch.com

 

[deadin]

So, hypothetically, if you design a barrel that is exactly long enough for the gasses from combustion to complete fully expanding at exactly the moment the bullet leaves the barrel, there should be no "slowing" of the bullet and it should be silent (as long as the bullet is sub-sonic.) All a suppresor does is slow the escaping gasses down to subsonic before they enter the atmosphere. This design would have no escaping gasses.

Of course if the barrel was a little too long of the gas expansion a little less, then you would have to contend with the "pop" like a cork being pulled out of a bottle.

 

[Mello]

deadin

So, hypothetically, if you design a barrel that is exactly long enough for the gasses from combustion to complete fully expanding at exactly the moment the bullet leaves the barrel, there should be no "slowing" of the bullet and it should be silent (as long as the bullet is sub-sonic.) All a suppresor does is slow the escaping gasses down to subsonic before they enter the atmosphere. This design would have no escaping gasses.

Nope.

In order for there to be "no slowing" of the bullet while it is in the barrel, there must be sufficient pressure behind the bullet to overcome friction and to keep moving the bullet out of the barrel.

Once the bullet exits the barrel that gas which was under pressure escapes from the muzzle and makes noise.

This made me think of the super canon project Saddam Husein had going during the Iran-Iraq war.
Iraq built a barrel with a bore of 350 mm (13.8 inches), and a barrel length of 46 metres (151 feet). It was supposed to have a range of over 400 miles.