black powder "peak?"

[caliber45]

Gents, this may run on a bit, and I apologize ahead of time. As a lead-in: modern smokeless propellants have varying burning rates, based on composition, granule shapes and other factors. A faster burning rate means a quicker "peak" -- the point at which the powder stops accelerating the projectile, and after which barrel friction and inertia begin to slow the acceleration of the projectile. Handguns need a faster burning propellant than rifles. Modern propellants burn, producing gas; black powder explodes, producing gas. Now, another lead-in before the question: I realize various makers of black powder use various ingredients, and that no two black powders are alike. There is no "standard" black powder. I'd like to eliminate that factor from my question. My question has to do with "generic" black powder (though no such animal exists . . .) peaking with various calibers. In other words, let's take .40 caliber as an example with Goex powder. Setting aside black powder variations by maker (as well as variants such as barrel makers, minute barrel dimensions, barrel composition materials, patch thickness/composition, etc., etc., etc., ad nauseam . . . is there a general "peak point" for that particular caliber at which X-amount of powder of FF powder reaches its full potential -- ie., at 36 inches of barrel -- and thereafter falls off? In other words, is a 36-inch barrel (or whatever) the theoretical "ideal" for that caliber, setting aside differences in powder ingredients, etc.? If so, are longer/shorter barrels "wasting" the potential of a particular caliber/powder combination. I've read various accounts (perhaps spurious . . .) of individuals trying increasingly heavier charges of powder in a particular rifle by firing it over snow . . . and then checking to see at what point unburned powder is evident on the snow at the muzzle. I don't want to get into a nit-picking, super-scientific discussion over this; just curious whether there is a "generic" peak-point for the various powder granulation/caliber combos. If you keep adding more and more powder do you keep getting more and more velocity (and a "longer" peak) until you blow the barrel, or is there a reasonable limitation? (I hope this thread doesn't get to be overloaded . . . I'm just curious. My brother asked me the question, and I didn't have an answer. -- paulallen, tucson az

[Skychief]

caliber45, great post.   I will be watching the replies here with interest.   Surely someone (smarter than me) can boil things down and we can realize where pressure ebbs and friction takes a grasp on our projectiles.   I assume your inquiry involves prb's in the different calibers, correct?

Thanks for clearly outlining a question I have pondered for too long!

Skychief.

[D. Taylor Sapergia]

Rather than a snow bank, I think you need a chronograph.  Then you can keep adding powder and recording velocities until those velocities begin to decline rather than to increase.  At that point, you are pushing powder which has become part of the projectile, rather than the fuel.  You will see, as you approach that point that you have to add much more powder to gain any increase in velocity, and at some point you will determine that adding more powder is a waste, for the increase in the velocity.
I for one do not have that information either remembered or recorded, because it does not interest me, and I think it's something that has to be done by the person interested, rather than relying on someone already having done it.

[Larry Pletcher]

With proper motivation and a barrel to waste, I'd tackle the problem a different way.  Staring with a typical load, I'd chronograph and cut off an inch.  Repeat and watch the velocity results.  Ideally you might see the velocity increase as a long barrel is shortened until you reach the point you are looking for.  After that the velocity would show decreases  as the barrel is shortened. 

This would be an interesting project and would yield worthwhile data. Any body have a barre to donate?   

Regards,
Pletch

[Mad Monk]

With proper motivation and a barrel to waste, I'd tackle the problem a different way.  Staring with a typical load, I'd chronograph and cut off an inch.  Repeat and watch the velocity results.  Ideally you might see the velocity increase as a long barrel is shortened until you reach the point you are looking for.  After that the velocity would show decreases  as the barrel is shortened. 

This would be an interesting project and would yield worthwhile data. Any body have a barre to donate?   

Regards,
Pletch

Pletch,

If you have access to a copy of the 1974 edition of the Lyman Black Powder Handbook you might want to take a look at it.

In the .36 caliber barrel they look at 28", 32", 37" and 43" barrel length.

A lot of data in there where you can relate barrel length to muzzle velocities where the only "variable" is the barrel length.

My copy has been worn to the point where it is rebound with multiple layers of tape.

Bill K.

[Mad Monk]

Pletch,

Something you might want to copy and file away.
Some might think it a bit of drifting off the thread topic.

The 1910 International Critical Tables gave a bunch of data on black powder.
One section that caught my interest was the theoretical potential energy of a typical "standard formulation black powder.  Expressed in pounds/feet per pound.
Which I converted over to grains weight.  As in ml charges.

So using their data a 100 grain (weight) charge of black powder will yield 13,100 lb/ft of potential energy.

Now.  The gun is simply a single-stroke heat engine.  You are using black powder as the fuel in this engine which you are then converting into kinetic energy in the projectile leaving the muzzle.  So when you look at the conversion of the potential energy into kinetic energy you are looking at a percent conversion.  This percent conversion being an indication of how effecient the gun is as an "engine".

So in my copy of the original Lyman Black Powder Handbook all of the velocity data has notes on percentage of energy conversion.  You can get some interesting data out of it.


Bill K.

[pulaski]

caliber45
The short answer is yes .There is a finite number , after that you are pushing unburnt powder and a projectile out the end of the barrel .
What that number is would be a long/lengthy physics calculation .
Steve

[Larry Pletcher]

Yah, just dug out my copy.  It's worn too, but I don't need the duct tape yet.  I thought I remembered a test like that but thought it was in an old Dixie Gun Works catalog.

Regards,
Pletch

[Daryl]

What we get, after a given amount of powder in a given barrel length, is less increase in velocity per grain of additional powder.  I think this is what Taylor was referring to.
At no point have I stopped getting an increase in velocity in my tests with increased charges. More powder develops higher speed.  It just takes more of it to get the same rate of speed increase, ie: 90gr. to 100gr., 40fps per 10 gr. increase. 100 to 110gr. dropping to 35fps increase, 120 to 130gr. dropping to 25fps increase, etc.- These are merely examples not actual recorded figures. But, the speed increases every time the charge in increased, albeit at reduced efficiency.  Does this mean the powder isn't burning - no.   

Taylor is correct in that a chronograph is necessary to see this. The chronograph will show you when the efficiency of the charge drops off.  Interestingly enough, this dropping off of velocity increases, happens with much heavier charges than most people today shoot.  As well, changing patch thickness, or ball diameter will also change the charge where this drop-off occurs.

Personally, I don't believe there is a charge anyone would consider using, that could spew unburnt black powder granuals out the muzzle. Shooting over snow, will show black specs of fouling on the snow with any load, easily mistaken for powder.  Afterall, 57% of it's volume is solid waste.

Trying to load to the best efficiency of the powder used, for me, would be wasted time on the chronograph. I am interested in finding the most accurate load for the rifle, not the most efficient load as to powder consumption.

Getting back to the initial question or notes concerning burn rates for different calibres or case sizes, we have the different granulations and to some extent different makes of powder.  In our muzzleloaders, hese take the place of the miriade of different burning rates of todays smokeless propellents. Generally, the smaller the bore, the finer the granulation used.  It does not hold true that the finer granulation will always give the highest velocity nor the best accuracy in any given bore size.  I've had rifles as small as .36, that preferred 2F over 3F. I also have a very accurate short range load for the 14 bore rifle, using 3F.

,

[caliber45]

Once again, thanks, guys. It is, as I figured, too complex and variable to produce any sort of "standard" rule-of-thumb. Being too lazy to pursue such research, and loath to squander my limited "fun" shooting time to such activity, I'll just accept the world-as-it-is, so to speak. Daryl put it as clearly as any: keep adding powder, you keep getting increased velocity. At some point, though, recoil and expense come into play, and at that point, adding more powder doesn't make sense. I guess that'll do it for me. Thanks again! -- paulallen, tucson az

[flintriflesmith]

What we get, after a given amount of powder in a given barrel length, is less increase in velocity per grain of additional powder.  I think this is what Taylor was referring to.
At no point have I stopped getting an increase in velocity in my tests with increased charges. More powder develops higher speed.  It just takes more of it to get the same rate of speed increase, ie: 90gr. to 100gr., 40fps per 10 gr. increase. 100 to 110gr. dropping to 35fps increase, 120 to 130gr. dropping to 25fps increase, etc.- These are merely examples not actual recorded figures. But, the speed increases every time the charge in increased, albeit at reduced efficiency.  Does this mean the powder isn't burning - no.   

...Afterall, 57% of it's volume is solid waste.

I think the measured difference in the increase in velocity per increase in charge is due in part to the fact that more powder creates more "solid waste" that also has to be accelerated out the bore.
Gary

[Larry Pletcher]

Daryl,
I'm guessing you and I were talking about two different things.  I agree that increasing the charge will result in increased velocity.  I was assuming the same load as the barrel is shortened.  If the only variable is barrel length, then we should be able to see velocity changes that relate to the original question. 

I think Bill Knight's comments about measuring the load efficiency is worth looking into using Lyman's data.  I started playing with that this morning.  I'm not ready to give an opinion on that yet.

Regards,
Pletch

[roundball]

As an aside...although BP is classified in the "explosives category"...my understanding is that BP does not actually explode any more than smokeless powder explodes.

It has a much lower ignition temperature for sure...and it burns extremely fast...a surface burner from the outside in, with different granulations producing different burn rates and subsequently different pressure curves...but BP does not detonate / explode like dynamite detonates / explodes.

If I'm all wet on this by all means point me to some official source documentaion to the contrary as I don't want to have a misunderstanding

[Mad Monk]

As an aside...although BP is classified in the "explosives category"...my understanding is that BP does not actually explode any more than smokeless powder explodes.

It has a much lower ignition temperature for sure...and it burns extremely fast...a surface burner from the outside in, with different granulations producing different burn rates and subsequently different pressure curves...but BP does not detonate / explode like dynamite detonates / explodes.

If I'm all wet on this by all means point me to some official source documentaion to the contrary as I don't want to have a misunderstanding

While OT here.

In comparing black powder to smokeless powders.
In open burn black powder is far faster than smokeless.  But under confinement smokeless burns way faster than black powder.  A lot faster!

You are correct in that black powder does not detonate.  Black powder is one of a number of composite explosives.  That means it is simply a mechanical mixture of the ingredients.  As such it is physically incapable of exhibiting true detonation.  The same is true of the commercial subs.  On the other hand.  Smokeless powders "without additions" is capable of low-order detonation.  The "additions" prevent this.  Even a 1 in a millon chance of detonation in a propellant powder is to be avoided simply do to the number of rounds fired in a year's time.

General rule of thumb is that heterogeneous explosives are incapable of entering into/exhibiting true detonation while homogeneous explosives are capable of true detonation.

Bill K.

[Dan]

Bill, I'm hoping you can clarify something for me.  I differentiate low and high velocity explosives based on the velocity of the shock wave, that being either subsonic or supersonic.  I think the term detonate is tied into that in some fashion but it is not clear to me what the significance is.  My recollection from days gone by is that even C4 has a "burn rate" of about 24,000 fps.  I'm guessing/interpreting your words to mean that BP deflagration remains subsonic, versus what may occur in smokeless powder in some circumstances?

I've always thought of them in terms of propellant/low velocity explosive in the past...

[Black Jaque Janaviac]

  I am sure there are limiting factors.  As powder increases you'll get a proportional increase in velocity.  Then, at some given charge you'll notice that the velocity gain was less than expected for the increase in charge.  This is known as the Point of Diminishing Returns (PODR).  For example say you get 100 fps gain every time you increase the charge by 10 grains.  Until finally going from 80 to 90 grains the velocity only increases 50 fps. 

My hypothesis for the board would be that (for black powder) increasing the barrel length will push that PODR up for a given caliber.   In other words say my above example was for a 28 inch barrel; if you increased the barrel length to 36 inches you might get a 100 fps gain going from 80 to 90 grains, but hit the PODR going from 90 to 100 grains.   And a 42 inch barrel might be able to digest a 110 grain charge before encountering the PODR.

I'm sure there's a point where the barrel just flat-out gets too long, but this probably is not experienced in a practical-length gun barrel. 

[Daryl]

 
Of course, with a powder that produces 57% of the charge as solid waste ie: 'ejecta', that 'amount' and therefore weight of fouling increases steadily when the charge increase & becomes extra weight to push out the barrel, which adds to the recoil.  That's a given.

[Larry Pletcher]

The graph below is based on the Lyman book that Bill Knight mentioned earlier.  Earlier he calculated the efficiency of a load and muzzle velocity based on Kinetic energy in black powder.

I ran the same numbers and graphed the results.  The chart is based on a 43" barrel in .36 caliber.  Loads were chronographed from 25 gr fffg to 70 grains.  The barrel was shortened to 37", 32", 28", and finally 20".  The efficiency of each load is graphed with the load at the borrom and the efficiency on the left.  If the decimals were moved two places to the right, the number would read in percents as in .1150 = 11.5%


The surprise to me is that in this caliber, the best efficiency was reached at 50 grains in each barrel length.  I expected it to be higher in the longer barrel lengths.  With sporting powders this might be true.

Regards,
Pletch

[Black Jaque Janaviac]

Larry,

Well so much for my hypothesis.  Although the 43-inch barrel exhibited a second increasing trend at the top end of the charges.  Would have been interesting to note what happens beyond that point.

Here's a quote I lifted from one of Daryl's posts on another thread that might be germain to this discussion. 

The base of the projectile must be as perfect as possible, so the powder gases last pushing it, do so as regularly as possible.  For this reason, we place the sprue pointing up.

Here Daryl is noting that exit pressure has an affect on accuracy.  I would venture a hypothesis that the longer barrel would have a lower exit pressure.  This would be more forgiving of blemishes in the base of the ball and possibly more accurate.

[Daryl]

Larry,

Well so much for my hypothesis.  Although the 43-inch barrel exhibited a second increasing trend at the top end of the charges.  Would have been interesting to note what happens beyond that point.

Here's a quote I lifted from one of Daryl's posts on another thread that might be germain to this discussion. 

The base of the projectile must be as perfect as possible, so the powder gases last pushing it, do so as regularly as possible.  For this reason, we place the sprue pointing up.

Here Daryl is noting that exit pressure has an affect on accuracy.  I would venture a hypothesis that the longer barrel would have a lower exit pressure.  This would be more forgiving of blemishes in the base of the ball and possibly more accurate.

BJJ - Exit pressure does have an effect on delivery of the projectile, even in smoothbores with very low muzzle pressures.  It is possible the lower the muzzle pressure, the greater the accuracy potential, however - the ball must be travelling at a speed and rotation that delivers best accuracy for that combination. I am not convinced that longer barrels are more accurate than short, as the longer the barrel, the greater the harmonics, wave movements of the barrel itself, which are injurious to accuracy if not exactly idential each shot.  The shorter a barrel, the stiffer it is, therefore less movement. Modern BR shooters found this out in the 1970's (or earlier) and most BR barrels are very short and stiff as a result.

I noticedthe upswing of efficiency as well.  It is quite possible there would be another peak around the 90 or 95gr. level but since no one uses these types of charges in that calibre - moot point, perhaps.

I also note there seems to be a leveling off after the post-peak dip in all barrel lengths longer than 20", which gives the indication that all of them might increase to another peak with heavier charges yet.

[Black Jaque Janaviac]

I am not convinced that longer barrels are more accurate than short, as the longer the barrel, the greater the harmonics, wave movements of the barrel itself, which are injurious to accuracy if not exactly idential each shot.  The shorter a barrel, the stiffer it is, therefore less movement. Modern BR shooters found this out in the 1970's (or earlier) and most BR barrels are very short and stiff as a result.

Did the modern BR shooter discover that shorter barrels were stiffer by nature?  Or did they discover, rather, that in order to properly stiffen up a longer barrel it would have to be impractically thick and heavy?  Know what I mean?

I wonder how much harmonics plays into longrifles though, given the lower black powder pressures, the full-stock wood and or barrel ribs, and the thick heavy barrels.

[longcruise]

Some are talking about incremental increases in velocity with incremental increase of powder while the original question was at what point would barrel length produce increased drag on the projectile that would overcome the forward propulsion of the projectile.  IOW, at what point in barrel lenght with a given charge would the projectile begin to slow before leaving the barrel?

I think with our commonly available barrel lengths that none would be long enough to test this.

[Jerry V Lape]

I believe the modern bench rest shooters in classes less than their unlimited class, are constrained by total weight limits imposed by the rules.  So in stiffening the barrels they chose shorter barrels but thicker as the route to stiffness within the weight allowed.  In recent years fluted barrels have appeared  as they reduce the extreme weight of very thick barrels without significantly reducing stiffness.  Benefits heat reduction too thru greater surface area on the barrel. 

[Daryl]

Weight certainly came into it with the BR boys.

As to barrel length and velocity, the short barrels, with very small powder charges can give higher speeds than the same load in a longer barrel. I guess what this means, is that to be efficient, the longer barrel needs more powder.

Check the .58 cal results in Lyman's book.  The 24" barrel gave higher velocity with heavier changes than did the 32" barrel, yet with smaller charges, the longer barrel gave slightly higher speeds - usually up to aound 50fps. Not at all you wouldexpect.

Instead of the piddly 1,077fps they achieved in the 24" barrel with 70gr. 2F GOX,  my 24" bl'd Musketoon delivers 1,340fps with 70gr. 2f GOEX using virtaully an identical ball and patch.

It's interesting that in some calibres, their figures are very close with today's powders, yet as in the .58's, they are way out of line.  Even in 1978, I recorded over 200fps higher velocities in my Hawken than they achieved in their Zouave barrel, yet I used a larger, heavier ball.  They recorded 1,506fps with 140gr.2f GOX using a .562", 260gr. ball and .015" patch which ran .006" larger than groove diameter, whereas I got 1,683fps with spit and 1,736fps with bear grease, using a .575", 275gr. ball ball and .022" patch. My combo was a bit tighter as .015 larger than the groove diameter.

Tests should be done over a range of powders in one's own rifle, to find out what's efficient and what shoots well. A cheap chronograph, like the Lee products is more than capable of showing what's going on.  Guesstimations don't work well and can present the wrong conclusions.

Regarding barrels so long as to retard velocity, I am not convinced you will see that, except perhaps with an exceptionally weak charge that spits the ball out the muzzle, ie: 10gr. powder in a .45 or 50 with a 40" bl.  In this case, a 20" barrel might be faster, making the 40" bl. slower - but only with that sort of a load no one uses.

[Larry Pletcher]

Regarding barrels so long as to retard velocity, I am not convinced you will see that, except perhaps with an exceptionally weak charge that spits the ball out the muzzle, ie: 10gr. powder in a .45 or 50 with a 40" bl.  In this case, a 20" barrel might be faster, making the 40" bl. slower - but only with that sort of a load no one uses.

Daryl,
Regarding this last paragraph, I really don't know the answer posed here, but I know how to test it.  I was thinking tonight that I wished I had a barrel to lop off 1 inch at a time and actually try this.  Then I thought that surely somebody has already done this.  I think I read about this - - maybe an old time shooter like Warner or Pope.   I think I've got to locate a book tomorrow.

Regards,
Pletch