[Graham Smith]

I shoot production and limited pistol so I have only been focused on the faster powders - because that's what everyone says to use. But I still don't understand the why of it all.

Over the weekend, I wanted to reset everything on my press to make sure it was right (been having some issues lately) so I dug out my "Competition Reloading with Brian Enos" DVD and watched him setup his 650 and made some notes. I was going to skip over the discussion of powders but thought it would be interesting to see what he had to say and it got me to thinking.

Given when the program was recorded, he was discussing major 9x21 and 38 Super and other calibers loaded to a 170PF. That's a lot of pressure. His powder of choice (at that time) was Accurate No 7 which has a good consistent medium burn rate (around 53 on one current chart I have). The reason for that powder was to get as much speed as possible with as little pressure. Thus choose a powder that burns constantly and, idealy, just finishes burning as the bullet leaves the barrel.

OK. That makes sense. Push the ball up the hill fast as opposed kicking it up the hill - same effort but spread over time or lower pressure spread over time. It also means that a longer barrel gives the powder more time to burn so a powder load that works in a 5" barrel may not work as well in a 4" barrel. Got it. This also helps explain why slower powders are better for compensators - you want the powder to still be burning to some degree when the bullet hits the compensator so that there is enough gas to "work" the compensator. Got that too.

But this also got me to wondering why the same theory would not work equally well for limited. Why the emphasis on fast powders? Would not a slower powder give you the same PF with less pressure and wouldn't that be preferable?

I suspect that the answers are buried somewhere in some thread (probably bits and pieces of a dozen threads), but I can't lay hands on it.

[TreblePlink]

Conventional wisdom with non-comp guns is to propel the projectile at design speed, but burn all the powder by the time it leaves the barrel to avoid further unnecessary "jetting" of gas which adds to felt recoil. This promotes faster sight return. Carry the idea too far with really fast powder and heavy bullets, and the peak pressures can get out of hand.

Graham Smith, on Sep 3 2009, 09:01 AM, said:

I shoot production and limited pistol so I have only been focused on the faster powders - because that's what everyone says to use. But I still don't understand the why of it all.

Over the weekend, I wanted to reset everything on my press to make sure it was right (been having some issues lately) so I dug out my "Competition Reloading with Brian Enos" DVD and watched him setup his 650 and made some notes. I was going to skip over the discussion of powders but thought it would be interesting to see what he had to say and it got me to thinking.

Given when the program was recorded, he was discussing major 9x21 and 38 Super and other calibers loaded to a 170PF. That's a lot of pressure. His powder of choice (at that time) was Accurate No 7 which has a good consistent medium burn rate (around 53 on one current chart I have). The reason for that powder was to get as much speed as possible with as little pressure. Thus choose a powder that burns constantly and, idealy, just finishes burning as the bullet leaves the barrel.

OK. That makes sense. Push the ball up the hill fast as opposed kicking it up the hill - same effort but spread over time or lower pressure spread over time. It also means that a longer barrel gives the powder more time to burn so a powder load that works in a 5" barrel may not work as well in a 4" barrel. Got it. This also helps explain why slower powders are better for compensators - you want the powder to still be burning to some degree when the bullet hits the compensator so that there is enough gas to "work" the compensator. Got that too.

But this also got me to wondering why the same theory would not work equally well for limited. Why the emphasis on fast powders? Would not a slower powder give you the same PF with less pressure and wouldn't that be preferable?

I suspect that the answers are buried somewhere in some thread (probably bits and pieces of a dozen threads), but I can't lay hands on it.

[Will Abrahams]

Leatham explained it as: faster powders shoot softer b/c there is less gas coming out of the barrel pushing the gun/slide back. He used some analogy comparing the end of the barrel to a rocket engine... less thrust coming out = less force...

I did a search for this a while back and remember finding a link to leathams site where he talks about it. i will see if i can find it for you.

[Graham Smith]

Will Abrahams, on Sep 3 2009, 12:50 PM, said:

Leatham explained it as: faster powders shoot softer b/c there is less gas coming out of the barrel pushing the gun/slide back. He used some analogy comparing the end of the barrel to a rocket engine... less thrust coming out = less force...

Less gas as in all the powder is burned before the bullet leaves the barrel. I follow that, but in listening to Brian talk about powder choice, it almost sounded as if he was saying the same thing about slower powders - you want something the expends all of it's energy inside the barrel but does so as slowly as possible.

So, if a powder like Red Dot (10) is really fast and Blue Dot (60) is in the burn speed range for a compensator, then it would seem as if something in the burn range of Unique (35) would be ideal for limited. But one of the most popular powders is N320 which is up around 17 on my chart.

It may just come down to there being a lot more choices now and things other than burn rate alone make the faster powders the better choice.

P.S. I chose these powders for burn rate comparison only - I don't want to get into which is the better powder argument.

This post has been edited by Graham Smith: 03 September 2009 - 10:43 AM

[XRe]

Graham Smith, on Sep 3 2009, 12:41 PM, said:

Less gas as in all the powder is burned before the bullet leaves the barrel.

No... this notion of "burned before the bullet leaves the barrel" is a red herring. So is any notion of "jetting" due to powder still being burnt as the bullet exits. Those things can cause other effects (like, a dirty load due to unburned powder, or a sandblasted comp, etc)

Quote

I follow that, but in listening to Brian talk about powder choice, it almost sounded as if he was saying the same thing about slower powders - you want something the expends all of it's energy inside the barrel but does so as slowly as possible.

(he's actually getting at load efficiency vs. burn rate, but that's a different thing - see below... also, old major was 175PF, so he was probably trying to get to 180PF..???)

Here is what matters - and there are a ton of threads on the forum where this is discussed a bunch

energy = m(v2) (mass times velocity squared), or, extended:

total recoil energy = m-bullet(v-bullet2) + m-gas(v-gas2) + m-unburned(v-unburned2) ...

The gas exits the gun at an extremely high rate of speed - 10,000 fps or, IIRC. That contributes significantly to the recoil energy in the system. The mass of the gas is proportionate (roughly equal to) the mass of the burned powder. The less powder you use, the less gas you create - and therefore the lower this component of recoil energy will be. Faster burning powder generally releases more energy for the same amount of mass vs. a slower powder - this results in lower recoil energy, as well, due to less gas exiting the barrel. There's no free lunch, though - at some point, you can create dangerous chamber pressures by running too fast a powder, and there can be catastrophic consequences....

It acts as a "rocket nozzle" simply because of the direction of the force vector - the gas tends to mostly exit straight out the barrel, unless its otherwise re-directed.

Open guns, on the other hand, want to use the energy in that gas stream for other purposes - pushing the gun forward and down. They also necessarily must operate at higher pressures than shooting minor PF in the same caliber. So, a slower powder is used for two purposes - one, to lower the chamber pressure to safe levels so that proper velocity can be achieved; and two, to create more gas to work the compensator and ports. There's a desire to have an efficient load - one that finishes burning the powder right as the bullet leaves the barrel, so there's no waste - but that's not required (in fact, the load I'm running is only about 85% efficient). And, you have to use a fast enough powder to push the bullet hard enough to get the right velocity before the pressure is uncorked and the powder stops burning (you can go too slow on the burn rate, and never make major). But, you can still notice the effect in an Open gun - the medium to medium-slow pistol powders will tend to make a softer shooting gun that flips some, whereas the slower powders will tend to make a flatter shooting gun that comes more straight back into the palm - but its a more complex system and those effects are not solely due to the mass of the powder being burnt.

That's probably a little over simplified, and one of the resident physics geeks will probably take some issue with it, but... there it is

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So, if a powder like Red Dot (10) is really fast and Blue Dot (60) is in the burn speed range for a compensator, then it would seem as if something in the burn range of Unique (35) would be ideal for limited. But one of the most popular powders is N320 which is up around 17 on my chart.

The above should help this make a bit more sense - N320 will have lower perceived recoil. Do a search on Clays powder for .40.... its super fast, super high pressure, and super soft to shoot.... and potentially super dangerous!

There's some evidence to suggest that slower powders may tend to be more accurate - somehow, the gentle push works better (perhaps more consistently) than the quick kick. But, we don't really need bullseye accuracy in this game, so most tend to bias toward what shoots softest/flattest/quickest for them, which tends to be a fast powder in an iron sight gun....

[D. Manley]

"CLICK" for Rob's Explanation.

[Jim Watson]

I understand the theory, but looking at the Accurate Arms book, you can get a 195 grain .40 to 880 fps (pf 171) with 4.6 grains of No 2 or 6.8 grains of No 7. The chamber pressure is the same.
No doubt the muzzle pressure will be lower with the fast burning No 2 and the mass of powder gas in the ejecta smaller. But it is 2.2 grains less. That is only 1.1% of the total mass departing the gun. Call it a 2% contributor, most recoil estimators assume the gas will blow by the bullet at higher velocity. That ain't much, what I call the Princess and The Pea Effect discernable only by the most sensitive.

Maybe somebody could explain it in terms of bullet acceleration or the buildup of acceleration itself. But that is Davis Mechanics which is WAY over my head.

[TreblePlink]

For a given velocity, with slow and fast powders, the MEAN pressure will be the same, but faster powders will have higher (sometimes much higher) PEAK pressure.

The most experienced shooters all seem to agree that for non-comped guns, fast powder and heavy projectiles are most competitive in our game. This may be a purely empirical and subjective "feel" factor.

The limit is safety - (Clays with heavy projectiles can Kaboom) You may notice heavy or "magnum" pistol loads will usually be prescribed with slow powders to minimize peak pressure.

Jim Watson, on Sep 3 2009, 04:42 PM, said:

I understand the theory, but looking at the Accurate Arms book, you can get a 195 grain .40 to 880 fps (pf 171) with 4.6 grains of No 2 or 6.8 grains of No 7. The chamber pressure is the same.
No doubt the muzzle pressure will be lower with the fast burning No 2 and the mass of powder gas in the ejecta smaller. But it is 2.2 grains less. That is only 1.1% of the total mass departing the gun. Call it a 2% contributor, most recoil estimators assume the gas will blow by the bullet at higher velocity. That ain't much, what I call the Princess and The Pea Effect discernable only by the most sensitive.

Maybe somebody could explain it in terms of bullet acceleration or the buildup of acceleration itself. But that is Davis Mechanics which is WAY over my head.

[XRe]

Jim Watson, on Sep 3 2009, 04:42 PM, said:

I understand the theory, but looking at the Accurate Arms book, you can get a 195 grain .40 to 880 fps (pf 171) with 4.6 grains of No 2 or 6.8 grains of No 7. The chamber pressure is the same.
No doubt the muzzle pressure will be lower with the fast burning No 2 and the mass of powder gas in the ejecta smaller. But it is 2.2 grains less. That is only 1.1% of the total mass departing the gun. Call it a 2% contributor, most recoil estimators assume the gas will blow by the bullet at higher velocity. That ain't much, what I call the Princess and The Pea Effect discernable only by the most sensitive.

Its not "mass leaving the gun", or even "momentum". Its "energy moving in a vector away from the shooter".

Assuming the gas is moving around 10,000 fps, as I've been told...

The bullet contributes 335.23 ft-lbs to the total energy.
4.6 grains of powder, now a gas moving fast: 1021.20 ft-lbs of energy
6.8 grains of powder, now a gas moving fast: 1509.60 ft-lbs of energy

That extra 2.2 grains of powder contributes 27% more energy to the equation (proportional to the difference in mass between the powder charges) - and more additional energy than just the bullet alone.

Remember, energy is directly proportional to the square of the velocity. Light things moving really fast have a lot of energy. Even if the gas is moving at half that speed (255.3 ft-lbs vs. 377.4 ft-lbs), it still increases the overall energy total by 20%.

edit to fix a math error

This post has been edited by XRe: 03 September 2009 - 03:17 PM

[XRe]

TreblePlink, on Sep 3 2009, 05:08 PM, said:

For a given velocity, with slow and fast powders, the MEAN pressure will be the same, but faster powders will have higher (sometimes much higher) PEAK pressure.
...
...
The limit is safety - (Clays with heavy projectiles can Kaboom) You may notice heavy or "magnum" pistol loads will usually be prescribed with slow powders to minimize peak pressure.

Good points, here.

Quote

The most experienced shooters all seem to agree that for non-comped guns, fast powder and heavy projectiles are most competitive in our game. This may be a purely empirical and subjective "feel" factor.

There's definitely at least some amount of "feel" involved - it depends upon the shooter's equipment platform, their temperament, and their skill level, too. For minor loads, for instance, some folks feel the 147gr 9mm stuff gets to be too slow and soft, and they like something just a bit snappier to the feel. So, they step back to a 125-ish grain bullet, usually with the same fast powder.

[Graham Smith]

XRe, on Sep 3 2009, 02:08 PM, said:

and there are a ton of threads on the forum where this is discussed a bunch

Yah, I've read and even printed out many of them. It just seems that suddenly, listening to Brian talking about pressure curves, the slow burn made sense but the fast burn didn't.

I think the key thing I've been missing all along is the idea that "The less powder you use, the less gas you create - and therefore the lower this component of recoil energy will be." It's the side effect of all that gas escaping that is beneficial in guns with a comp and detrimental in those without. Which also explains a lot of why you want a light weight bullet traveling very fast for open vs a heavy bullet traveling slower - the lighter bullet needs more powder to make it go faster and more powder means more gas - or more energy that can be harnessed to do something besides move the bullet.

Finally, I think it all makes sense. For a production or limited gun, the powder has only one job - move the bullet. With an open gun, the powder has two jobs - move the bullet and provide lateral thrust to stabilize the barrel.

This also helps explain why small calibers are preferable to larger calibers in open guns.

This post has been edited by Graham Smith: 04 September 2009 - 06:32 AM