black powder "peak?"

[Skychief]

Pletch, I for one hope you will do some experimenting about this subject as I know you would be quite capable of making sense out of the question!     Surely somewhere in this world a barrel exist just waiting to be lopped off an inch at a time behind a chronograph.   Would you be willing to experiment and post results if a barrel is found?

[Larry Pletcher]

This sounds like a worthwhile experiment.  It's 9 degrees here this morning, this sounds like a summer project.  I haven't had a chance to speak with the other half of Chapman/Pletcher Engineering too. 

As far as logistics go a long barrel would be needed and I'd think it would be helpful if it would fit through the headstock of Steve's lathe.  I'm sure we could just whack it off but an ability to cut a quick crown might keep us from damaging a patch.  A damaged patch could play hob with consistent velocities. 

I really need to run this past Steve.
Regards,
Pletch

[Daryl]

Really wouldn't need sights or a stock, Larry.  Maybe Hugh would lend you his machine rest?

[northmn]

Dixie Gun Works lopped off a 40 cal barrel in the manner you are questioning and generally found a decrease in velocity as the barrel was cut off.  The trend is also shown in the Lyman catalog mentioned. when I chronographed some loads I found that with my 50 cal there was a point where the velocity gain with 3f was limited.  With an additional 10 grains the gain was maybe 60 fps or so.  I quit at that point because I believe that a roundball reaches its maximum efficiency somewhere around 1800 -2000 fps.  A pure lead projectile may not retain its integrity at higher velocities and its downrange gains become increasingly limited as the air resistance also increases geometrically with velocity. From a theoretical standpoint where one did not care about fouling, or practical gains I would not know if if or where an increase in powder charge would decrease velocity. There used to be a theory about using faster burning smokeless powders in pistol and shotguns with shorter barrels.  Tests showed that even in 2 inch barreled handguns, velocities could be increased with slow burning powders like 2400.  One writer commented that it may be like race cars vs economy cars, a race car may not be "efficient" in that they burn a lot of fuel but they are faster.  Economy is not the issue.

DP

[Mad Monk]

  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. 

I am fairly certain that the point of diminishing returns relates to the burn rate of the powder in a particular size bore.

To better explain that.

If you look at original rifles that still have the original tin charger you see in something like a .44 caliber you have a gunsmith made tin charger that throws just about a grain per caliber.  Roughly 45 grains for a .44 or .45 caliber rifle.  These guns were usually shot using a very fast burning sporting powder at that time.

Most of the data out there now was generated using du Pont and then GOEX black powder.  If you look at a can you see it described as a "rifle" powder.

If you go back to the 1800's.  Up until the end of the Civil War you see three distinct types of black powder being produced for use in small arms.  You had a very fast, very hot burning sporting powder.  Used mainly in the guns up to .50 caliber.  Above .50 caliber you would see a "rifle" type powder being used.  At .58 caliber you would see a "musket" powder being used.  Each powder fit into a specific burn rate range.  And by burn rate as it applies here it refers to the actual combustion of the powder separate from any grain size considerations.
The differences between the 3 types related to the "quality" of the ingredients used and the length of time they would be run in the wheel mill.

When the Swiss sporting burn rate powder first came onto the U.S. market I looked at it in my .45 caliber patched ball rifles.  It showed this point of diminishing returns around 43 to 44 grains in the .45.  In the .50 caliber patched ball rifle it was around 55 grains.

Basically, a sporting burn rate powder gives this p.o.d.r. at about 1 grain per caliber.  A rifle powder around 1.5 grains per caliber and a musket powder around 1.6 grains per caliber.

The old writings on black powder mention what they called the "expansive force" in a powder charge.  The very fast, very hot sporting powders gave the most expansive force per unit of weight.  A rifle powder gave less expansive force and a musket powder even less of this expansive force.

If you shot a musket burn rate powder in a .36 caliber you had to use a lot of it to get a workable velocity with a lot of bore fouling as a result.  At the same time if you tried to shoot the very fast, very hot sporting powder in something like a .69 caliber musket it would really hurt the shoulder and give you a lot of blow by in the gun.  They tailored the chemical burn rate of the powder to more or less match the projectile mass being used.  Balancing the volume of gases produced.  The rate at which they are evolved by the burning powder and the temperature of the gases evolved.  All of this added up to this expansive force thing.

This p.o.d.r. thing is even seen in the early bp cartridges.  The original .45-70 cartridge was designed around Civil War surplus musket powder.  NOT a rifle burn rate powder.  So the p.o.d.r. in a .45 with a musket burn rate powder is 70 grains.  The cartridge originally designed around the rifle burn rate powder was a .45-60.  The oriinal .44-40 artridge was designed around the very fast sporting powders of the day.


Bill K.

[Mike R]

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

I know I have seen an experiment published where the barrel was progressively cut off.  Can't remember where--maybe  Bevel Bros in MB mag?

[Larry Pletcher]

Mike, all,
I found the chart that Mike and I were thinking of.  Dixie did the test years ago.
They started with a .40 cal., 40 inch barrel and cut it of in 2" increments.  They did 5 shot strings and recorded the average for a barrel charge and barrel length.  The chart is found yet in teh back of teh catalog under "Velocity Data".

I didn't reproduce the chart here but may use Bill K's efficiency formula on it tonight.  A quick look shows what looks like fuzzy numbers to me.  Reading the chart horizontally things look reasonable.  Reading the chart vertically looks inconsistent.  I wondered if two different people did the loading (seating pressure) or weren't consistent about wiping between shots.   I am curious about others thoughts.
Regards,
Pletch

[Daryl]

In testing both the .58 and the .69 rifles, if I wiped between shots using spit for lube, I got the same outrageous shot to shot velocity variations that I got with bear grease. 

Shooting 'dirty' without wiping in both those same guns, resulted in shot to shot extremes of less than 10fps in 10 shots - usually 4 to 8.

Outrageous results for me when wiping between shots with spit for lube as well as shooting dirty with grease patches, the extremes ran into the 20's to 30 fps variation over 10 shots.  I didn't see any point in wiping when using the grease as shot to shot velcoties were out to lunch, in comparrison, in my opinion.  Of course, modern rifles do well with only 20 to 25fps extremes.

[longcruise]

There is a page on the Rice Barrel site where the barrel was incrementally cut off and velocities checked.  Here is the link:

http://www.ricebarrels.com/velocity%20test.html

[Larry Pletcher]

Mike,
Thanks for the Rice link.  That makes 3 different sources of data where the barrel was cut in segments and velocities were recorded.  All together Ive run numbers in the Lyman, Dixie and now Rice experiments.  Steve  Chapman has  book we'll look at written by Mann.  I seem to remember a similar experiment in his book.
Looking at the 3 mentioned above, I believe the change in numbers we were looking for is smaller than the variation in the velocities collected.  Instead of a predictable rise in efficiency to a peak and then a decline, we are more likely to see "up and down" variations bigger than the expected result.  Trends are visible but that is about all.

When you think about it, we were comparing barrel length to efficiency, but there numerous other variables that affect efficiency: seating pressure, patch/ball combination, lube, etc.   Even if results were uniform, a change in caliber, or any other change and we're back to square 1.   

A more useful experiment IMHO would be to take your own fixed length barrel and chorongraph  different loads and simply graph the velocities.  You will run into the same variations but a trend is perhaps enough.   Trying to reach a conclusion that is valid for all calibers and barrel lengths is probably chasing windmills.

Regards,
Pletch

[northmn]

Like Daryl, I found that I got results that varied more with wiping between shots when I chronographed.  Also had to let the load "foul in" with a couple of shots.  Another thought on this issue kind of occurred to me if you look at BP cartridges.  When smokeless came out the 30-30 shot about 1900 with a 165 grain bullet, and the European cartridges about 2200 or so.  they could gt about 1900 with jacketed bullets and BP but with some rather compressed loading techniques as in the 303 Brit and a Turkish cartridge.  About the most the lead bullet cartridges were getting was about 1600 or a little more.  The gains from the 45-70 to say the 45 120 (45 - 3 1/4) were not outstanding, and were best acquired with he use of the heaviest bullets.  The 45 Colt, loaded with BP was not chambered in rifles, but the claims were that it really gained little with a longer barrel over a pistol, something like about 150 fps.  The 44-40 was better suited for rifles for reasons I am not going into here, but because it also could get more gain and gave about 1300fps.  These were in quite long barrels and not the carbine versions.  The 45-70's gain over the 45 colt was due to heavier bullets.  While round ball can be driven over 2000 fps, the round ball is so inefficient that that advantage was negated at any longer range.  Higher velocities in BP cartridge guns were never really achieved, even when extra long cases were used.  Again the law of diminishing returns.  Realize also that a BPC does not have any leak in the ignition system or blow by around a patch.

DP 

[Mad Monk]

I need to correct something in my posting of yesterday.

A sporting powder gives a p.o.d.r. at 1 grain per caliber.
Rifle powder at 1.4 grains per caliber.
A musket powder at roughly 1.5 grains per caliber.

Bill K.