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- Thread starter peterdobson
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The infographic is self-contradictory.
If the powder is all burnt by about 5", then how could a longer or shorter barrel influence how "fast" the powder should be? Either way, the powder will be all burnt, so what does the last 10" of barrel have to do with what happens in the first 5" ?
If the powder is all burnt by about 5", then how could a longer or shorter barrel influence how "fast" the powder should be? Either way, the powder will be all burnt, so what does the last 10" of barrel have to do with what happens in the first 5" ?
Looking at the graph consider what happens to velocity if the barrel was shorter. The velocity would be lower. So to compensate increase the burn rate to move the all burnt position closer to the chamber. Effectively allowing the projectile in the shorter barrel to achieve a higher velocity to a point. Optimizing burnt rate, barrel length and projectile weight together can maximize velocity.
This approach is limited by the maximum safe chamber pressure.
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The powder may be burned in 5" but the gas produced is till pressurized and pushing against the base of the bullet until it exits the muzzle.
Sure, but once it is burned, the gas from powder A is the same as the gas from powder B, no?
Define "same".
Volume of gas and the speed at which it is produced will vary, basically the difference between fast and slow powders.
The gas from burnt powder will continue to expand until the pressure reduces to a certain point of stasis, where the pressure exerted is less than whatever opposes it (the bullet).
In the barrel, because the bullet can’t exert enough restraint to contain it, the pressure is traded inversely for velocity. After the powder is completely burnt it does mean the velocity ceases; it means the rate of of velocity increase slors down.
In the barrel, because the bullet can’t exert enough restraint to contain it, the pressure is traded inversely for velocity. After the powder is completely burnt it does mean the velocity ceases; it means the rate of of velocity increase slors down.
This^^^
After all the propellant is burnt, as long as the force exerted by the pressure inside the barrel is greater than the combined forces of atmospheric pressure and friction of the bullet against the bore, the bullet will continue to accelerate down the barrel at a diminishing rate of acceleration.
In theory it will do this until the forces balance and it stops. In practice, until it leaves the barrel while still accelerating. The only instance I can think of when the bullet would stop in the barrel is a squib load.
In which way? The powder that provides the highest velocity in a long barrel will also give the highest velocity in a shorter barrel. Faster burning powders can’t make up the difference at the same max pressure. Or maybe you’re referring to something other than velocity?
The gasses may well be the same (samish) but there is the matter of larger charges of slower burning powder simply having a larger volume of gas trying to go down the same hole.
Longer barrels are a great dietary source of free velocity
This.
I'm just having trouble seeing how what you describe is good for a 26" barrel but not good for a 16" barrel. In both barrel lengths we have a larger volume of gas pushing the bullet until it exits, whether it exits at 16" or 26".
A larger charge of slow burning powder at the same max pressure will give higher velocity in the 16” barrel too. It might have a muzzle flash that can seen from low earth orbit, but right up to that point it’s still pushing harder, longer.
A term often thrown around is “area under the curve”.
The pressure that generates enough force to launch the bullet is lower than the maximum possible pressure from all the powder being burned in the casing. This is why powder still burns in the barrel , since the bullet is already accelerating down the bore.
If the powder has a slow enough rate of burn, and the barrel is short enough, the bullet will leave the muzzle before complete combustion, and unburnt/burning powder will be ejected behind it. This means that you get incomplete energy transfer, and therefore don't achieve max MV and waste powder.
So, conversely, you'd need a faster powder to achieve near complete combustion in a short barrel, to maximize the energy transferred onto the bullet in it's short time in the barrel.
I do think you are right that a 16 to 24" barrel won't make THAT much difference, but a pistol-length barrel vs. a rifle length one will.
I see what you’re saying; when it comes down to it all the text is just a collectof words
You have a point. I’m not sure the graph and list of random factors and characteristics and variables listed on the side bar without explanation do. Maybe the secretary made it?
