Factors Affecting Muzzle Velocity – Round 1

[WadePatton]

Couple of observations wrt the cupped breech plug.  I can only think of three things the cupped face does (that could be credited for more velocity):   moves the ignition point slightly fwd (easy to test), increases the effective length of bbl very slightly, improves combustion chamber shape (it's a hemi!  ).

And while i have great respect for the work of Keith, I'm thinking that the ignition point change is too subtle and that the "chamber" shape is the underlying cause for performance enhancement.  Such that a flat surface would receive all pressure equally, but that a curved surface does not, that it "deflects" (or whatever most appropriate term) the forces somewhat and that the this gives a better push to the ball.

IOW less energy is expended on the curved surface than would be a flat surface--the "bonus" energy pushes harder on the ball.  

Those are my internal ballistical thoughts, although it's the effects that count mostest.



(No more flat faces here   )



Also, IIRC someone somewhere at sometime made a spring-loaded compression measuring/limiting device to accurately repeat loading compression.  I would think such should be employed in this testing for better control of that important variable.  cheers and thanks!

[Joe S]

I can only think of three things the cupped face does (that could be credited for more velocity):   moves the ignition point slightly fwd (easy to test), increases the effective length of bbl very slightly, improves combustion chamber shape

We know what the effect of lengthening the barrel is – roughly speaking, velocity increases about 10 feet/second/inch.  The increase in length with the cupped breech plug was only 0.2” so we can eliminate that hypothesis.

The other two ideas, changing where the powder column is ignited, and the “hemi” effect are easily testable.  All you would need to do is drill three flash holes, one near the breech plug face, one in the middle of the powder column, and one near the forward edge of the column.  Plug up the two holes you aren’t using and start the test.

I hope somebody does this test.  I would really like to know the answer, but I’m not likely to do it for a couple of reasons:

1.  Even if moving the flash hole forward increases muzzle velocity, I’m not going to do that on a gun.  Aesthetic issues of lock placement outweigh any advantage in velocity that might be gained.

2.  I’m not sure what Dan would say if I drilled all those holes in his barrel, but it’s not too hard to guess.  Dan lives in a small town in Montana, and as you might expect, the bulk of his vocabulary consists of words that have only four letters.

The question about load compression force is right at the top of my list of experiments to do next.    Hunting season and winter are upon us, so as soon as the snow melts out in the spring, I’ll get after it.  Spring here is July most years, although sometimes it doesn’t get here until mid August or so.

[Larry Pletcher]

The question about load compression force is right at the top of my list of experiments to do next.    Hunting season and winter are upon us, so as soon as the snow melts out in the spring, I’ll get after it.  Spring here is July most years, although sometimes it doesn’t get here until mid August or so.

Steve Chapman and I did a load compression test using an adjustable collar on the bench rod to produce repeatable levels of compression.  Our purpose was to test a theory (not ours) that percussion guns likes compression but flint guns did not.

I'm not sure if it's what you have in mind, but it might.

http://www.blackpowdermag.com/load-compression-and-accuracy/

Regards,
Pletch

[Joe S]

Pletch

Very interesting.

Do you have the data from the chronograph?  I would like to take a look at it if you do.  That could give me a lot of insight as to how to conduct another experiment.

What I had in mind was seating the ball with different pressures, and measuring muzzle velocity.  The idea is that if muzzle velocity doesn’t change across a range of loading pressures, then accuracy is not likely to change either.  Conversely, a change in velocity would suggest there may be a change in accuracy.  We would want to look at mean velocity and variability in velocity as well.

I like the way you used compression depth rather than a compression force like I had in mind.  Force is going to vary depending on patch/ball/lube combination, condition of the barrel etc., but compression depth gives you an absolute repeatable measurement. 

As far as an experiment design, I would probably do 5 shots at several intervals and use regression analysis, plus 15-20 shots at the extreme ends to look at variability. 

My only critique of your experiment is that 25 yards may be too close to pick up differences in accuracy.  Sometimes things that look similar at 25 yards look very different at 100 yards.

[T*O*F]

Joe,
You might want to try Swiss powder in your experiments.  When I chronographed a long range rifle using it, the standard deviation was less than 12 fps between shots.  This might tighten up the results you are getting with other powders.

[Dphariss]

In BPCR the powder charge needs to be settled to the same level every time its better to add or take away a little powder than to vary the compression. But in a ML unless powder fouling changes the volume this would not be a problem and using a scale to give uniform compression force should work fine in a ML where seating depth is not an issue.  Also the compressive pressure available to the ML shooter is a small fraction of that available to the BRCR shooter with a loading press.
If the charge is the same and the compression varies much so will the velocity. If the charge is the same an the density varies so will the velocity since flame spread through the charge is changed and thus the burn rate.
This is why serious slug gun shooters and others use a drop tube in the barrel. A drop tube when the powder is poured through at a consistent and slow rate it will pack the powder to a uniform density  in the barrel. This promotes uniform flame spread in the charge and uniform velocities. But even then if the charge is not compressed the same, usually about .030 to .060 is a cartridge the velocity will change. If dropped inconsistently then compressed to the same level  as it would be with a compression die in BPCR shooting the Standard Deviation may go from 5-8 fps to 30-40. So if going for minimum velocity variation this is just one of several things to worry about.  One other is having a uniform amount of lube and etc etc.
This is of limited importance to the general RB shooter but if trying to reduce variables in testing they must be addressed.
Dan

[Larry Pletcher]

Joe,
We wrote the chronograph reading on the target for each shot we fired.  We wanted a record that pared a reading with the shot location.  I know I stored the targets for a while, but now I'm not sure where they are.  I will try to find them.  Also I know I had a crib sheet while we worked.  That may be around here.

At the end of the article we listed a few changes we intended to use, because we wanted to redo the experiment. We thought a 50 yard target, Redfield Olympic sights, weighed powder charges and culled balls would eliminate variables.  We threw this test together pretty fast. 

We were watching compression vs group size when using percussion and flint.

[Larry Pletcher]

I found the targets - 4 flint and 4 percussion - one each for each compression test.  Each target has a line drawn from a hole to the chronograph reading.  A number also tells the order of the shots within that group. 

Private message on the way.

Regards,
Pletch

[Joe S]

T*O*F

Thanks.  I’ll see if I can finds some Swiss somewhere.  I have a very strong suspicion that a lot of the unexplained variability we see in black powder shooting is due to the powder itself.

[Bob Roller]

Right after GOEX started marketing black powder under their own name,the late Tom Dawson tried to use some to regulate both barrels of a double 500 #2 and using his chronograph was able to determine that velocity excursions (variances)made the task impossible.He called GOEX and was told that they were aiming at a market that had no idea what a fine double barreled rifle was and were happy if the gun they had went off.
In other words,the idea of quality control from batch to batch wasn't on the schedule.
We got much better powder later on from GOEX and as far as I know,it is still good powder.The Swiss may or may not be better but the Swiss are noted for high levels of quality control in other things than gunpowders.
 Uniform loading techniques with a round ball muzzle loader or long range type is the key to accuracy.The same goes for black powder cartridge rifles used in competition.Ball/bullet weights and compression of the charge will tell the story IF the barrel is any good and crowned properly.

Bob Roller

[T*O*F]

Right after GOEX started marketing black powder under their own name

I think you mean to say marketing Goex powder of their own manufacture.  Prior to that, they marketed Curtis and Harvey powder under the Goex brand name.

[Bob Roller]

It was DuPont and then GOEX. C&H quit producing when their mill blew up in 1971.
I still have DuPont and C&H.Also a can of 4fg from E.M.Farris's shop in Portsmouth Ohio
and I think it is from King's powder Co.

Bob Roller

[Dphariss]

Right after GOEX started marketing black powder under their own name

I think you mean to say marketing Goex powder of their own manufacture.  Prior to that, they marketed Curtis and Harvey powder under the Goex brand name.

Like Bob said:
C&H would not have met the military spec for their contracts.  The C&H available here in the 60s and 70s was made in a blasting powder plant in Scotland and was pretty poor stuff, this is why it took a lot of powder to get the same velocity as Dupont-GOI-Goex   these three were made at the same plant at Moosic. Dupont never stopped making powder in the US. Largely because the military uses BP in fuses and boosters. Thus the military kept the production alive after Dupont destroyed all the other plants and when there was little call for BP. GOI then bought the plant then it became GOEX after it sold again. 
When they finally really blew the Moosic plant up with parts landing in the nearby town they moved to Louisiana.

Dan

[Daryl]

and further from any town? just wondering