How Much Powder Is Too Much

[George]

Why do you think it is "counterintuitive" ?

Ha, caught me! That's my polite way of saying I don't believe it.

Spence

 

[Ontario47]

Barrel full of BP:

 

[George]

Not interested??? 14.7 pounds per square inch pressure is created by the weight of a column of air 1" square base X the height of the earth's atmosphere (about 62 miles). Once the pressure at the powder chamber of a gun has fallen to 14.7 lbs there is no reason for the leftover gasses to move (at the speed of sound) in or out disregarding leftover vibration of the barrel,

That's absolutely right, not interested, because the way you describe it is exactly the way I understand it.

Nothing about that description explains what is supposed to create negative pressure. Or maybe I'm missing something....do you know what they are thinking of?

Spence

 

[Ontario47]

If you had some magic gun powder that would accelerate a bullet fast enough to make it out of the barrel at the same time NOT producing enough combustion gas (at standard temp and pressure -14.7psi) to fill the volume of the barrel there would be some vacuum created as the bullet slowed down but had enough inertia to make it out of the barrel (not flint breach). Now does regular muzzle blast (after the bullet is gone) have enough inertia to create some vacuum??? Just talking produces air movement at the speed of sound, it doesn't take much force to start and stop the air movement. The little inertia left in the gas at the end of the muzzle blast has slowed to the point where it can't overcome almost any of the outside air pressure so the pressure at the breach does not drop below what ever the atmosphere is. What ever the air pressure is on the frontal area of the gun it is equal to the pressure on the rear area. All of the recoil is due to the acceleration of the bullet, unburned powder, and blast gasses and their combined inertia.

 

[Carbon 6]

Now does regular muzzle blast (after the bullet is gone) have enough inertia to create some vacuum??? Just talking produces air movement at the speed of sound, it doesn't take much force to start and stop the air movement. The little inertia left in the gas at the end of the muzzle blast has slowed to the point where it can't overcome almost any of the outside air pressure so the pressure at the breach does not drop below what ever the atmosphere is.

I think it does have enough inertia if you have the velocity. Especially if you look at high speed film footage.

 

[Zonie]

That's absolutely right, not interested, because the way you describe it is exactly the way I understand it.

Nothing about that description explains what is supposed to create negative pressure. Or maybe I'm missing something....do you know what they are thinking of?

Spence

OK. You asked for it.
First off, when we were talking about 14.7 psi, that would assume that there was a complete vacuum with 0.0 psi pressure. It will never drop that low in a gun barrel.

As we know, a gas has mass or weight to it. Like all things with mass, once it is moving, it doesn't want to stop moving.
When the powder burns, the high pressure forces the projectile out of the bore and the gas itself also moves out of the bore at a high velocity. As the high pressure gas leaves the barrel, there is nothing behind it to replace it so the pressure inside the bore drops to a negative pressure, forming a vacuum. Not a huge vacuum but the pressure inside the barrel is less than atmospheric pressure.
As the powder gas has now left the bore, fresh air under normal atmospheric pressure rushes back into the bore to replace the lower pressure of the vacuum and when it hits the breech plug, it will create a (very) small force adding a little bit to the recoil of the gun.

This same high pressure, high speed gas making a negative pressure (vacuum) phenomenon was used by the Germans to make their "pulse jet" V1 engine run. It is also used in racing engines in cars, boats and motorcycles.
In these engines, when the high pressure/high speed exhaust gas reaches the end of the exhaust pipe or reaches an area where the exhaust pipe suddenly gets larger, it also creates a negative pressure wave (it is a vacuum) that travels back up the exhaust pipe towards the exhaust valve or in the case of a 2 stroke engine, the exhaust port.
In a 4 stoke engine, at the end of the exhaust cycle, there is a time when both the exhaust valve and the intake valve are slightly open.
If the tuner has done his job right, that negative pressure wave will pass thru the still open exhaust valve and enter the combustion chamber creating a negative pressure at the intake valve. That sucks more air/fuel mixture into the cylinder than would normally happen if the pressure wave got there too soon or too late.
How well it works is all a matter of timing so the length of the exhaust and the speed the engine is running at must be made to work while the engine is running at a speed where it would produce the most power.
In a 2 stroke engine, the same thing happens and because both the exhaust port and the inlet ports in the engine are open at the same time, the results can be huge. Think of the 2 stroke dirt bike with a "tuned exhaust" on it. At low engine speeds it is very docile but when it reaches a certain higher speed, all H. breaks loose and the front wheel climes for the sky as the rear wheel throws dirt behind it in a rooster tail.

This is the basis for the "tuned exhaust" you may have heard of.

And now folks, let get back to talking about "How Much Powder is Too Much?"

 

[George]

Well, as I exit this thread, please color me a nonbeliever.

Spence

 

[Carbon 6]

OK. You asked for it.
First off, when we were talking about 14.7 psi, that would assume that there was a complete vacuum with 0.0 psi pressure. It will never drop that low in a gun barrel.

As we know, a gas has mass or weight to it. Like all things with mass, once it is moving, it doesn't want to stop moving.
When the powder burns, the high pressure forces the projectile out of the bore and the gas itself also moves out of the bore at a high velocity. As the high pressure gas leaves the barrel, there is nothing behind it to replace it so the pressure inside the bore drops to a negative pressure, forming a vacuum. Not a huge vacuum but the pressure inside the barrel is less than atmospheric pressure.
As the powder gas has now left the bore, fresh air under normal atmospheric pressure rushes back into the bore to replace the lower pressure of the vacuum and when it hits the breech plug, it will create a (very) small force adding a little bit to the recoil of the gun.

This same high pressure, high speed gas making a negative pressure (vacuum) phenomenon was used by the Germans to make their "pulse jet" V1 engine run. It is also used in racing engines in cars, boats and motorcycles.
In these engines, when the high pressure/high speed exhaust gas reaches the end of the exhaust pipe or reaches an area where the exhaust pipe suddenly gets larger, it also creates a negative pressure wave (it is a vacuum) that travels back up the exhaust pipe towards the exhaust valve or in the case of a 2 stroke engine, the exhaust port.
In a 4 stoke engine, at the end of the exhaust cycle, there is a time when both the exhaust valve and the intake valve are slightly open.
If the tuner has done his job right, that negative pressure wave will pass thru the still open exhaust valve and enter the combustion chamber creating a negative pressure at the intake valve. That sucks more air/fuel mixture into the cylinder than would normally happen if the pressure wave got there too soon or too late.
How well it works is all a matter of timing so the length of the exhaust and the speed the engine is running at must be made to work while the engine is running at a speed where it would produce the most power.
In a 2 stroke engine, the same thing happens and because both the exhaust port and the inlet ports in the engine are open at the same time, the results can be huge. Think of the 2 stroke dirt bike with a "tuned exhaust" on it. At low engine speeds it is very docile but when it reaches a certain higher speed, all H. breaks loose and the front wheel climes for the sky as the rear wheel throws dirt behind it in a rooster tail.

This is the basis for the "tuned exhaust" you may have heard of.

And now folks, let get back to talking about "How Much Powder is Too Much?"

Never thought I'd see the day when you and I agreed on something .

Think of the 2 stroke dirt bike with a "tuned exhaust" on it. At low engine speeds it is very docile but when it reaches a certain higher speed, all H. breaks loose and the front wheel climes for the sky as the rear wheel throws dirt behind it in a rooster tail.

Sounds like my first attempt to pull a wheelie on one, the power band kicked in and away went the bike and there I stood.

 

[GREENSWLDE]

Hi Zonie. Your theses on tuned exhausts has been proved many times . Even to megaphones on 4 strokes. I have used tuning on racing outboards in ye past as well as on 4 stroke bikes and even on Austin 7 side valve engines.(750 M/C in the 50's and 60's). I had never thought of it with M/L's. I have always gone back to basics. A white sheet and count the unburnt powder from the muzzle. Seems to work for me.. 65grns C&H No.2 with a 425 Lyman 452121 usually gives fair results at 100 yds Can I have my "Y" back ?? for GREENSW"Y"LDE. Stay well, OLD DOG

 

[tenngun]

I guarantee you that adding 50 grains of powder will produce a lot more recoil than adding 50 grains of dead lead.

Recoil isn’t just the mass of the ejecta but also the velocity of the ejecta. Just as you increase the velocity you also increase the energy of the projectile. The recoil is equal to the ejecta.
If you drive a .36 up to 2200 fps you get about 750 ft pounds, and you get that velocity on top of about 70 grains.
A 40to 50 grain charge in a .54 will get you about 750 lbs.
Your ejecta in the .36 will be about 130 grains. In the .54 your ejecta is 260 grains.
But your .36 is likely to be a lighter gun, so your perceived recoil may be less in the .54

 

[GREENSWLDE]

My 9.6 mm R/B was ways Sonic at 100 yds with 40 grains of C & H No.2 with .385 ball and .010 cotton(ex p/j s) patches