slower powders = higher velocities

B

Billglass

New member
Is it a proven fact, or inherent in the design of smokeless powders, that slower powders produce higher velocities than faster powders? Or is it just a general rule that may have some exceptions.

I'll restrict the question to revolvers because I'm also curious if a significant amount of "energy" is lost out the cylinder gap with shorter bullets and slower powders. (for an example a 125 grain bullet shot out of a 357 using a powder like H110)

I've posted this on The Shooters Forum as well
 
There is certainly a lot of energy lost out the cylinder gap and muzzle, more out of the muzzle of short barrels. But the "slower" (higher charge weight for maximum pressure) have more to spare and will give higher velocity at all barrel lengths.

A good many years ago, a gunzine writer tested the idea and confirmed the advantage of slow burnng powders in a 2" .357 Magnum.
But then he applied the human factor and went to a powder and load that gave less blast and flash, accepting the lower velocity. He was still getting more power than any .38 Special load out of any revolver.
 
My experience is that there is an ideal burn rate range for a given cartridge which will eke out the best velocity.

A ridiculous example is the 357 magnum loaded with bullseye on one end of the spectrum and IMR4831 on the other end of the spectrum. Ignition issues aside, I don't think that the 4831 cartridge will perform as well as one powered by an intermediate powder such as 2400, found on a burn rate chart somewhere in between those two other choices.
 
I have found that powders that fill the case with little or no ccompression at or near max are best in a given caliber. For .357 mag that has been 2400. For .308 IMR 4064 fits the bill. .270 win its IMR 4350. You can't go with too slow of a powder because then you cannot fit enough in the case to get desired results. With some caveats what you are saying is generally true.
 
There is a little bit of a red herring with the general rule of slower powders vs velocity when you restrict it to handguns,particularly short barreled handguns.

I say that because a short handgun barrel just does not allow enough time/distance for a pressure curve/acceleration.

In the extreme,for illustration only,I do not think H-4831 (a slow rifle powder) will give much velocity in a 45 ACP.Actually,one of the fastest powders,Bullseye,will give decent velocity from a 45 ACP.

There are a number of parameters working.

The maximum suitable pressure is one.

Expansion ratio is another...long explanation,you might look it up.It has to do with the cartridge case volume vs bore dia,or how rapidly the volume of the total combustion chamber expands as the bullet moves through the bore.

Contrast the 45 ACP to a 25-06.

Case capacity vs compressed load,

The list goes on.

Your general rule of slower powder equals higher velocity,I would contest.

We have a broad spectrum of powder burn rates so we can optimize a pressure curve for our particular application.

OOPS!! Stubbycat was writing faster!! He beat me to it!! We said the same thing.
 
There's so many variables with reloading, it's kind of hard to put any totally reliable rules to it.
That's why so many replies to questions on the subject begin with "It all depends." :)
 
I would say that the key factors for a particular caliber are barrel length and bullet weight. A short barrel doesn't give a slow powder time to develop optimum pressure. A heavier bullet has more mass and therefore more inertia as well more bearing surface and therefore more friction. A heavier crimp also comes into play in the same way. These factors decrease the time to peak pressure.
 
Is it a proven fact, or inherent in the design of smokeless powders, that slower powders produce higher velocities than faster powders?
Click to expand...

Hodgdon's website shows loads for 13 or so powders with the 357 125 gr bullet. Hodgdon's data is tested and proven.
Hodgdon also has a powder burn rate chart.
H110 is one of the slowest powders that Hodgdon lists for that combination, and it yields the highest velocities at accepted pressure levels. Hodgdon sells lots of other powders that are slower burning than H110. Those powders are too slow to equal H110 velocities in the 357.
Same goes for Alliant and Accurate powders, etc.
Same results are found in reloading manuals from bullet manufacturers.
If you want top velocity from a 357 revolver, you're going to have to use something a lot like H110.
 
There are some powders so slow that people have successfully used them as "filler" in big bore cases.

In any given firearm there will be a total volume of chamber and bore before the bullet leaves the muzzle. On a revolver the cylinder gap also bleeds off energy.

You want a powder that is close to 100% burn in the available volume to maximize pressure that gets turned into velocity. Going slower than that burn rate will hurt velocity. Going much faster than that burn rate won't help velocity.

Jimro
 
Its a guideline....but as others have said, its not a guaranteed rule.

You just need to spend some time reviewing the burn rate chart..and the loading tables from Hodgdon.

Part of the fun of reloading...is picking your load to do what you want it to do....less recoil, more velocity, etc.../ having said that, I tend to stick with one powder in my handgun loads ( Hodgdon TiteGroup )...in .380, 9mm, .40 S&W, .45 acp, .38 spl, .357 mag and .44mag....because it meets my needs.

But try some different published options and have fun with it...figure out what you want your loads to do. ( but never go below published min / or over published max ) ...
 
Higher octane gasoline burns slower than lower octane gasoline; but it has the potential to deliver more energy. It's kind of the same thing with smokeless powder.

When the primer is set off, a lot of dynamics come into play. When loaded properly, a slower powder gives a more sustained burn. It takes a little more time to get a bullet to go a little more faster - slower powder is better at achieving such a task. A lot of other factors come into play, but that's the foundation of it.

Getting more specific, H-110 will get a 125gn bullet roaring down the barrel of your revolver. In terms of sheer velocity, it'll likely outperform a faster powder in most situations.

So why not just use a slow powder for just about every round of ammunition? The answer is: "reality." Again, there are a lot of variables; and probably even more applications. Hence, the wide array of powders.

I load a lot of 125 grain jacketed hollow points for my 357 magnum revolvers. I never use H-110. Why? Because of the aforementioned reality. I usually shoot a 3" or 4" barrel 357. I find H-110 - although quite capable of delivering high velocities - has the drawback of producing a great deal of report (explosive noise), muzzle flash, and thrusting recoil. That's not what I'm looking for in my ammunition. Moving to a faster propellant such as Power Pistol, will give me 95% as much velocity with much less of the report, flash, & recoil. To me, that is a more than fair trade off.

If I was loading for my 8-3/8" bbl 357 Mag (a safe queen these days), then yes, maybe I'll go with the super slow powder. And if I had a lever action carbine in 357 Mag (I wish I did) I would most definitely go with the H-110.

It's what I call building ammo that is "balanced" for the gun.

Getting to the barrel/cylinder gap: It bleeds off a significant amount of energy. But it is what it is and it isn't really something to factor in when selecting a propellant for a given application.
 
Nick
What's so different about power pistol.

I notice in Lyman 49th, it's a faster powder than 2400, yet it achieves 1 fps more at a lower pressure?
 
Billglas,you might be overthinking it.

The burn charts are useful to select appropriate powders..."in the zone"

But they are not useful to predict performance.Too many variables!!.Powders perform different at 48.000 psi than they do at 52,000 psi.Some are "peaky" They give sharp pressure spikes as pressure increases.Some are more linear .

If you are searching for some "rules" you can use to place internal ballistics in order...It just does not work that way.

Another bad analogy is drag racing.There is not one simple rule,even horsepower.Assume the track length (barrel lengh) changes.Torque vs RPM? Broad versus narrow powerband? Gearing? Shift points" Traction? Burn rate,pressure.

While isolating one variable and making one change at a time is a good way to make improvement,every change interacts with a number of other variables.

It gets a little complex to predict,so we test and measure results against assumptions.

I can think of one issue that can turn up for revolvers,cylinder gap,high pressure,slow powders.Some cartridges/loads will gas cut the top strap of the frame.

As far as the difference between Power Pistol and 2400....Well,just guessing,about 6oyears of powder evolution? Elmer was using 2400,when,in the 50's? Its one of the older powders.Useful,versatile,great performance.
I get the 8 lb jug.
Power Pistol??When did it come out,and for what market? I don't know,but,lately!!.Its a great Major Power three gun and IPSC powder.10 mm,460 Rowland...Some powders are designed to gas comps.

Its also hard to find.(Power Pistol) Those who believe in Power Pistol might make do with HS-6 or Longshot because there is no PP on the shelf.
 
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My experience is more with rifles than handguns, and it depends on bullet weight. In all of the cartridges I load for the heavier the bullet used, the slower the powder you need to get top end speeds. As bullet weight drops then you start seeing better results with faster powders.
 
Rifle is a far easier place to see this. You have ultra slow powders for super magnum high velocity cartridges that might even fail to properly work on a small ,22 cartridge, and something like 2400 is almost destined to be useless in some of the ultra mags. Again, numerous variables, but within a certain level of variables, you will find a band of proper performance, and either up or down the chart will start to fade in performance, not only in velocity, but possibly accuracy, consistency, and other possible negatives.
 
Is it a proven fact, or inherent in the design of smokeless powders, that slower powders produce higher velocities than faster powders?
Click to expand...

GENERALLY speaking, the slowest powder that will burn completely will produce the highest velocities, but once you get into powders so slow that they start burning powder in the air after the bullet has exited, you start losing velocity, again.
 
Thank you all for your replies so far

Let me add, I am posing these questions considering a 357 magnum revolver with 3 to 6 inch barrel lengths in mind.

And I should also add, as SSA mentions, that when I consider burn rate, it's just within each powder companies selection and just for those powders considered appropriate for the firearm

Such as a selection of Alliant's Bullseye, unique, power pistol, and 2400

Or Hodgdon's hp38, hs6 hs7 and h110

I would think that within those groups of 4 powders, their burn rate ranking is clearly distinct.
I would agree, trying to use the "all inclusive" burn rate chart would have way too many variables to come up with some sort of general rule.

SSA
I noticed in Hodgdon’s data for 125 grain bullet and H110 that the test gun had a 10 inch barrel! So that would explain the lower velocities chrono results we would see with 3 to 6 inch barrels

HiBC
Yes, I know I’m overthinking it. I appreciate the honesty. These questions come from discussions I’ve been having with a fellow re-loader. I’m just trying get more information.

My curiosity regarding the cylinder gap with shorter bullet and slower powders is because, I've seen chrono data with velocities 300 fps lower than book velocities for full charges of H110 and 125 grain fmj's
they were not my handloads
heck it may have been from just not enough crimp -

but could the cylinder gap and longer exposure account for this difference?
Lyman 49th data uses a universal receiver.....does it have a gap?


Maybe the info added here reduces some of the variables.
 
Good post HiIBC.

What's so different about Power Pistol.?

I notice in Lyman 49th, it's a faster powder than 2400, yet it achieves 1 fps more at a lower pressure?
Click to expand...

I suppose we're getting off the subject. But since you're the OP, it's okay :p.
I was just using Power Pistol as an example in my post. But I do use it a lot for the application. I like 2400 too and it's what I use for my 158 grain boomers. Power Pistol is a relatively modern, high-energy propellant that's a derivative of Bullseye, and is absolutely identical in appearance. It used to be called BE-84 - BE, as in BullsEye. Anyway, it is good stuff and quite useful in a lot of applications. Particularly useful for hot semi-auto rounds. But as HiBC alluded, it is one of those "peaky" powders (I use the term "spikey") and I tend to shy away from recommending it for novice loaders. It can spike on you if you're not careful during the work up process - as can Bullseye; probably not a coincidence. But I digress . . .

Why PP outperforms 2400 according to Lyman 49th? Because that is the result that Lyman got. Your mileage may vary ("YMMV"). As I mentioned in my first post: there are a lot of variables. PP is definitely faster than 2400. And when I need a slow propellant (which isn't often), I reach for 2400.

I think it's important here to not overthink this (as HiBC said). It's not a perfect universe. Variables abound. Just because something seems to be a certain way on paper, doesn't mean it is in reality. As loaders, we are faced with a lot of contradictions and peculiarities. The trick is to not get too wrapped around the axle over them. And there is no substitute for doing your own work ups, with your own guns, and document your own results. (I strongly recommend a chronograph, if you don't have one.)

You're obviously new to TFL (welcome, btw). How long have you been loading? It would seem you have a type of ammo in mind to load (357/125). What is your goal and purpose for this ammo? What gun(s) do you have? And more specifically, what barrel length? Components (especially powder) can be a bit difficult to find. Do you have powder? Bullets? Where are you in the loading process?
 
Billglass,Correct!! Universal receivers with test bbls have no gap,and unless you are shooting something like a Contender,these velocities are not realistic.
 
considering a 357 magnum revolver with 3 to 6 inch barrel lengths in mind.
Click to expand...

I didn't see your most recent post until after my most recent post.

There is a big difference between a 357 with a 3" bbl, compared to a 6" bbl. They are quite different animals. I have S&W 686's in 3", 4", & 8-3/8"; plus, a Python in 6". The way they behave with the same ammo is quite different.

What will be the primary purpose for this gun? (carry? home defense? hunting?) Any special considerations? (arthritis? the shakes, etc.)

I carry my 3" 686. I use my 4" in competition. I punch a lot of holes in paper (shoot recreationally) with both. My other two 357s spend a lot of time keeping each-other company in a safe.

So for me, I'm shooting relatively shorter barreled 357 Mags. That is a major factor in my powder selection. All else being equal, loading with a shorter barreled gun means shifting your powder choice toward the faster stuff. Bullet weight is also a major factor. Lighter bullets shift your powder choice toward the faster stuff too.

Although I shoot with 3" & 4" bbl guns, I tend toward heavier bullets. I prefer 158's (but still shoot my share of 125's).

So with 158's, I usually use HS-6 or Power Pistol. If I'm going a little hotter, I use AA#7. I do use 2400 a little bit, but it's kind of a novelty thing; as the report, flash, & recoil are excessive (in my opinion). And the 2400-loaded rounds almost never see the 3" bbl gun - it's just silliness with such a short barrel.

With 125's, my powder selection shifts toward faster stuff - albeit with some overlap. I usually use AA#5, Unique, or Power Pistol. But never HS-6, AA#7, or especially, 2400. If I'm taking a longer barreled gun to the range, then yes, maybe I'll load up some 125's with slower stuff; as the longer barrel will tame the report, flash, & recoil - and convert it to velocity ;)

That just kind of gives you a feel of one long-time (32 years) loader's approach. I'm not saying you must use these powders for those bullet weights. I'm just demonstrating how it's typically approached.
 
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