Does increased pressure equal higher fps?

[Jason313]

I am curious to know this as I am considering a snub nose 1860 army but I know short barrell with black powder means less power, so my question is if reaming the Chambers out to a bigger diameter, say with groove depth comes out to .447, then ream Chambers to ,451 so more pressure is built pushing it through the forcing cone, and out the barrel, it's a 3 inch barrel,

 

[Jason313]

 

[paul harm]

Your powder burn is going to be limited with a short barrel. Maybe you could chronograph the velocity of a 3" and a 8" barrel and let us know.

 

[rodwha]

By increasing the friction it would indeed increase the pressure and in turn increase the velocity typically. See what happens when this fellow uses the same charge but a larger ball:

http://poconoshooting.com/blackpowderballistics.html

I’ve been told by a fellow who created a snubby and tested it found that 3.5” was needed to get a complete burn. But by this it appeared to mean that none was found on the sheet in front of him. I figure that could easily mean some of the powder could easily have burned outside of the barrel and was consumed before it hit the sheet.

The more bearing surface creating friction, along with weight that takes more to get it propelled, will create more pressure.

One fellow found that he achieved a higher velocity with a 180 grn Ball Et vs a ball with the same powder charge. However in his .36 cal his heavier bullet did not go quite as fast as a ball.

 

[labnoti]

Just remember that pressure happens over time. It is not just a number. We often consider the number for "peak pressure" because the chamber has a pressure limit. But it is the area under the pressure/time curve that produces velocity. So if you increase the maximum pressure or increase the time the pressure is applied, provided you're not reducing the time under pressure or the peak pressure respectively, so the effect is greater area under the pressure/time curve, velocity will go up. Practically, you can do those things by using more powder or using a longer barrel. Since using more powder will also increase your maximum pressure, there is an upper limit to how much more powder you can add before you reach the chamber's limit. However, you can continue to increase the area under the pressure curve by adding pressure over time. This is done with more of a slower burning powder, and a longer barrel.

 

[whughett]

Ok his whole discussion is way above my head, but doesn't black go from a solid to a gas in one kaboom, not much time element there, while smokeless, and its measured burning rates have a much longer peak pressure curve, if black goes kaboom the time in barrel would have more effect than a graphed power curve. So longer barrels can create higher velocities simple because the push is longer. And then there is that whole barrel gap thing in a revolver.

 

[rodwha]

Ok his whole discussion is way above my head, but doesn't black go from a solid to a gas in one kaboom, not much time element there, while smokeless, and its measured burning rates have a much longer peak pressure curve, if black goes kaboom the time in barrel would have more effect than a graphed power curve. So longer barrels can create higher velocities simple because the push is longer. And then there is that whole barrel gap thing in a revolver.

Not that I fully understand it all, but no. If it did there wouldn’t be discussions on finding unburnt powders even from rifles. However it is not quite the progressive thing smokeless is.

 

[Loyalist Dave]

Ok his whole discussion is way above my head, but doesn't black go from a solid to a gas in one kaboom, not much time element there, while smokeless, and its measured burning rates have a much longer peak pressure curve, if black goes kaboom the time in barrel would have more effect than a graphed power curve.

AH, No...., if there was no difference in the rate of deflagration, then switching from 1Fg to 2fg and from 2Fg to 3Fg would not increase velocities in loads.
Yes smokeless powder does have a burn rate too, and it accelerates under pressure, and the pressures reached far exceed what one gets with black powder.

LD

 

[whughett]

Ok, I see my error, kaboom and the push is all you get, a controlled burn and the velocity keeps increasing as long as the projectile is in the barrel. So the ability to release its energy is different in the kernel sizes of the various granulations of black, and the burn longer as the granulation size goes down.?
One of the handles here posted a burn chart sometime back on just this subject.

 

[paul harm]

It seems rodwha answered the OP's question with his link. Or not. If the chambers are reamed, is a larger ball going to be used or is it just done to increase the powder charge ? In rodwha's link it appears going to a bigger, or should we say heavier ball, increases pressure. They're all reduced to chamber diameter so it would seem to reason it's because one is heavier than another. Now here's the question. Does the heavier ball create more pressure because it takes more to get it going, or the resistance from the forcing cone, or both ? Personally the small difference doesn't matter to me enough to over come the difference in loading pressure needed trying to seat the ball. And I don't think reaming the chambers would make all that much difference in performance. Good luck in what ever you decide.

 

[rodwha]

It seems rodwha answered the OP's question with his link. Or not. If the chambers are reamed, is a larger ball going to be used or is it just done to increase the powder charge ? In rodwha's link it appears going to a bigger, or should we say heavier ball, increases pressure. They're all reduced to chamber diameter so it would seem to reason it's because one is heavier than another. Now here's the question. Does the heavier ball create more pressure because it takes more to get it going, or the resistance from the forcing cone, or both ? Personally the small difference doesn't matter to me enough to over come the difference in loading pressure needed trying to seat the ball. And I don't think reaming the chambers would make all that much difference in performance. Good luck in what ever you decide.

Those who ream the chambers tend to be match shooters, and they tend to claim it improves the accuracy. The tiny increase in volume couldn’t amount to much more than a grain or two of powder. We see modern lead bullets are always 0.001” over groove diameter. I couldn’t say why exactly having it set up this way makes enough difference to do it, but it seems to. They wouldn’t bother if it didn’t.

Seeing a difference (usually but not always) seems to not just be the weight but the additional bearing surface created when seating and shaving lead. Weight and bearing surface create friction that attempts to defy moving allowing the powder to burn just that little bit longer creating more pressure from what I understand.

Since friction is necessary to keep the projectile on the powder one would ideally want to use a slightly larger ball than chamber diameter. More tends to be better.

I wonder if relying obturation steals a bit somehow.

 

[Jason313]

It seems rodwha answered the OP's question with his link. Or not. If the chambers are reamed, is a larger ball going to be used or is it just done to increase the powder charge ? In rodwha's link it appears going to a bigger, or should we say heavier ball, increases pressure. They're all reduced to chamber diameter so it would seem to reason it's because one is heavier than another. Now here's the question. Does the heavier ball create more pressure because it takes more to get it going, or the resistance from the forcing cone, or both ? Personally the small difference doesn't matter to me enough to over come the difference in loading pressure needed trying to seat the ball. And I don't think reaming the chambers would make all that much difference in performance. Good luck in what ever you decide.

Perhaps I'm oversimplifying it but my thinking is that if the size of the chamber and therefore the size of the projectile is larger than the size of the barrel grooves then just like a power nozzle does to water it would increase the pressure coming through the "nozzle" of the Forcing cone. Yes/no maybe?

 

[Pete D.]

Velocity is a result of pressure and time. The longer that any pressure is applied, the faster the object will go. Ion engines on deep space probes are a classic example....thrust is measured in millinewtons but is applied nonstop....the craft continues to accelerate.
Bullets in guns will accelerate until pressure stops. Once it leaves the barrel, it is slowing down.

 

[shunka]

....but doesn't black go from a solid to a gas in one kaboom, not much time element there, while smokeless, and its measured burning rates have a much longer peak pressure curve......

not exactly
perhaps this pressure vs time chart (altho in a 12 ga ) might help?
yhs
shunka

 

[shunka]

I am curious to know this as I am considering a snub nose 1860 army but I know short barrell with black powder means less power, so my question is if reaming the Chambers out to a bigger diameter, say with groove depth comes out to .447, then ream Chambers to ,451 so more pressure is built pushing it through the forcing cone, and out the barrel, it's a 3 inch barrel,

My Good Jason.
to answer your question, I can relate that several acquantences have that very snubby.
by loading the chambers as full as they could with triple 7 and using a 200-225 gr conical lead bullet, they
consistantly achieved slightly over 700 fps without modifying the chambers.
hope this helps
shunka

 

[grter]

My question is at what point will the gains of increased become diminished when using black powder.

 

[Mizar]

Apart from reaming the chambers, which I think is a must for one looking for optimal performance, because I simply don't believe in the "swagged & obturating balls" theory - chrony data proves that wrong I believe, no matter what people say. You can try reduced charges with 4fg powder behind a LEE 220 grains conical bullet - it's a faster burning powder and the bullet is heavy and with more bearing surface than a round ball, so one gets a better powder burn and higher pressures from the start. From my researches on the subject a safe charge with 4fg will be about 20 to 25 grains for a 1860 pattern revolver.