breech pressure

[red-demon652]

Any one with lots of experince shold be able to this one. Will a longer barrel ultimately build higher preshure than a shorter barrel with the same load? {This should get a good debate.}

 

[Jim Watson]

No.
No debate, just no.

 

[Maverick223]

Nope, the longer barrel will continue to hold pressure for a longer period of time, but the pressure decreases from the moment the bullet moves, therefore barrel length is of no consequence to chamber pressure (at the breach or anywhere else).

 

[red-demon652]

Yes i do belive you put in in prospective maverick223 i never realy thought of it that way till now.

 

[wanderinwalker]

No.
No debate, just no.

^ This ^

Common misconception. Barrel length is meaningless to chamber pressure. Falls into the same category as "use faster burning powders for maximum velocity in shorter barrels" or "a .357 snub-nose is only a loud .38."

(Both of which are wrong too, for what it's worth. Maximum speed is acheived by burning the largest amounts of the slowest powder that works at the chamber pressures of the cartridge in question. And burning more powder will give more velocity, regardless of barrel length, which is why a .300 Magnum with a 20" barrel will outrun a .308 with a 20" barrel, even though the .308 is technically more efficient with the shorter tube.)

 

[BrocLuno]

However, the total pressure curve is different than straight chamber pressure. There is a reason that .357 out of a saddle gun is faster than out of a 6" revolver. There is more time for the overall pressure curve to act on the projectile and accelerate it.

There is a reason the military's put 26" to 30" barrels on rifles in the old days, it was to get maximum velocity out of the available powder. They wanted to take maximum advantage of the pressure curve and use all the powder.

Chamber pressure is related to initial ignition and the spike in the pressure curve related to the smallest volume. Once the projectile starts moving, the spike is over as the volume increases. That does not mean that all pressure is gone, it may be less than initial (chamber pressure), but it is still higher than atmospheric and friction, so it still accelerates that bullet.