Barrel length/pressure relationship

jimmy.jet

jimmy.jet

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If the same components are used will a 38 special load fired through a 3" or 1 7/8" barrel develop more or less pressure than the same load fired through 6" barrel?
Previous threads suggest lower velocity in shorter barrels but I found none dealing with pressure.
 
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No difference. What pressure is made in the short barrel is the same as the long one except its vented sooner when the bullet exits. This is why the loss in velocity wit a shorter barrel.

Kind of like the fast powder for short barrels. Faster velocities can be achieved with slower powders even in a short barrel. Don't just believer me, look in the manuals and try it for your self.

David
 
The short answer is, with everything else being equal, the short barrels develop less pressure. But more doesn't mean higher. The reason the other threads talk about velocity and not pressure is because they are using a chronograph to measure velocities, but they have no reliable way to measure pressure.

The long answer is real long, is there something specific you are wanting to find out?
 
Jellybean said:
The short answer is, with everything else being equal, the short barrels develop less pressure. But more doesn't mean higher. The reason the other threads talk about velocity and not pressure is because they are using a chronograph to measure velocities, but they have no reliable way to measure pressure.

The long answer is real long, is there something specific you are wanting to find out?
Click to expand...

Not true. The pressures are the same, determined at the chamber. The diff is how long the pressure/gasses stay in the bbl. There are reliable ways for the home ammo maker to measure pressures, just have to buy the gear.
 
Maybe Jellybean is trying to say there is more total area under the pressure curve with a long bbl ? To take a stab at long ago physics : the (similar) pressure acting upon an object for a long time period imparts more work aka energy. But in the firearms context when pressure is discussed, almost always it is peak chamber pressure being discussed.

There are a number of dimentional factors that can effect chamber pressure , but other than redicously short ( like a bbl that ends just past the case mouth ) bbl length isn't one.
 
in the very short barrels I will give you a definite maybe.
the combustion cycle starts at 0 psi, makes a rapid trip to max for the load, then declines back to zero.
if that max pressure point occurs while the bullet is at the 2" mark, it will be released prior to the peak in the 1 7/8" barrel.
Where 38 special is concerned, it wont make any difference.
357 magnum might, however, due to its slower burn rate powders
 
If you have over pressure loads the cyl/chamber goes bang, the barrel NEVER bursts from an over pressure load. Why bbl length only comes into play as regards to pressure vs vel. A longer bbl allows the gas to continue to expand, but peak pressure happens at or just after ignition.
 
4227 is an interesting powder.
It delivers the goods in magnums but it tends to leave a good bit of unburnt powder behind.
I have to wonder if that is not because of the pressure drop at the cylinder gap before it reaches peak
 
With typical handgun loads, both H110 and Bullseye reach peek pressure in less than 1/2" of projectile travel. That is 1/2" from case mouth, not from start of barrel

Just look at a pressure curve generated from any of the piezo-electric pressure systems. They will show pressure over time. You should be able to google one of more.

The Ohler PBL was a comsumer affordable system that measured velocity and pressure
 
Peak pressure in a revolver is generated in the cylinder, not in the barrel. As colt saa said, by the time the bullet is all the way into the barrel, the pressure is dropping. Look at any pressure curve. You can even see the drop where the bullet leaves the cylinder and a huge drop where it leaves the barrel.
And for the "it seems to me crowd", I'm NOT guessing; I've looked at actual pressure data.

Added: If you want to check the math also http://e-ballistics.com/ebook/internal%20ballistics%20-%20pressure%20gradient.htm
 
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this popcorn still needs a little more salt ...
Just how, exactly, do they measure and subsequently chart the position of the bullet in real time?
Or, do they compute it?
Seems to me that the practice would be awfully hard on expensive data logging equipment.
Can't question the pressure trace portion of the data. with piezo electric transducers, its within reach of the long standing and proven technology of Digital Storage Oscilloscopes.
 
For those looking for data, here's what Quickload says:

For a 9mm, 115gr FMJRN, default cartridge length and other parameters, 5.2gr HP38:

1.5" barrel: Max pressure 31876psi, 814fps
2.0" barrel: Max pressure 31876psi, 947fps
4.0" barrel: Max pressure 31876psi, 1170fps

So peak pressure is unchanged, muzzle velocity changes due to time under power. Like from a standing start holding your accelerator to the floor for 1.5sec, 2.0sec, or 4.0sec . . . same max HP and torque, different speed when power is finally removed.
 
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