Compressing BP Charges

[Oyeboten]

TheRodDoc recently posted a mention of how compression BP might break up the Granules into 'fines' which would alter the conflagration rate.

I do not know, but I thought this was an interesting mention.


Such BP Loadings as I have done, whether in Cap & Ball Revolver, or, Metallic Cartridge, I compress the BeJeeeZez out of the Powder.


What all do we know about this?


Is there an optimum amount of compression?


What happens if one merely seats the Projectile onto the Powder with no gap, but, does not do any compression?

Can one over-compress by normal Loading Lever means, or via a light re-loading Press worth of leverage?

 

[Curator]

My understanding of compression in black powder cartridges is that it limits the extent to which theprimer flame penetrates into the charge. If the primer only ignites the back end, the compressed charge travels down the barrel with the bullet, initially acting as a "filler" preventing gas leakage past the bullet until the pressure is sufficient for obturation to take place. Compressed charges should burn slower but at higher pressure and also cleaner. Looser charges don't do this, and accuracy suffers. One of the problems with bottle-necked black powder cases was the poor accuracy they exhibited with their uncompressed charges as compared to straight and tapered cases.

 

[Oyeboten]

Thanks Curator,



I would image there is a little less available Atmospheric Oxygen in a compressed Charge, than in one which is not compressed...which would possibly moderate the rate of conflagration.


I would still like to know what difference there would be if 4F were used instead of 3F in Metallic Cartridge Revolver, especially for small size/Caliber Cartridges - would it burn faster? make more pressure? Less? Same?

A compressed Charge of 4F would have to have even less available Atmospheric Oxygen than one of 3 F...but, I would also think the smaller particle size would have a faster rate of conflagration.


Of course, we have all heard or read about over-pressures occuring when an air Space is inadvertently allowed between Bullet and Powder, whether or not there is any common knowledge about why an over-pressure would occur from this.

Too much Atmospheric Oxygen available? Promoting too fast a conflagration?

 

[mykeal]

Black powder supplies it's own oxygen, like all explosives. The presence or lack of atmospheric oxygen has little to do with the rate or amount of gas that's generated.

4f burns both faster and a bit hotter than 3f. Assuming the same chemical mass is consumed the amount of gas will be the same, but the higher speed of deflagration will cause a higher pressure spike. The pressure generation curve will be shorter in duration, thus releasing the same amount of energy.

The smaller particle size is the reason 4f burns faster and hotter, but it's because the contact area between the particles is greater, not because the air space between the particles is smaller. When one particle burns it transmits the heat to adjacent particles faster if they're closer to it, and if there are more of them the chain reaction is faster. With larger 'chunks' the contact area between particles is smaller, plus there's a larger gap for the heat to have to transmit where the particles are not touching.

The large air gap problem occurs because it allows a shock wave to form. A shock wave is by definition a large pressure discontinuity, or pressure spike. This shock wave does not form in the packed powder column because it is a much denser medium than air, and thus has a higher speed of sound.

 

[Oyeboten]

Hi mykeal,



Thank you...makes sense.


Any conjecture on whether 4F may be used for Short Barrelled Revolvers, ( or part 4F, part 3F ) as in say, a 2 Inch, or, 3 Inch Barrel .45 Colt? where a little faster conflagration would maybe be a plus? Or would it be dangerous for possibly making too much Pressure?

 

[ClemBert]

I also read TheRedDoc's opinion that black powder doesn't compress it only crushes. I have no doubt that at some point, with enough pressure, that granules will crush. But how much pressure is required is beyond me. I read a thread one time where some fella did an experiment to see if granules are being crushed during normal loading and compression of BP. I wish I could find the link to the thread, but alas, I can not. Don't take my word for it but I thought the outcome was that very little granule crushing occured. It seems to be accepted by most sources that BP does compress. Again, how much compression before granules crush would be an interesting experiment. Compression yields better velocity, accuracy, and cleaner burning....or so they say.

In any case, there seems to be a number of retailers who sell a "compression plug" to allow reloaders to compress their BP. For example:

Buffalo Arms: "Many shooters are finding an increase in accuracy and clean burning characteristics by compressing their Black Powder Cartridge loads .200"-.400"."

Some interesting reading: Introduction to Black Powder Cartridge Rifle Loading

 

[Oyeboten]

I have merely been using the Bullet Seating step for compressing the Powder...seems to work fine, although a dedicated Compressing 'Plug' would likely be better, if adding an additional step.



What about the use of 4F in Metallic Cartridges slated for Short Barrel Revolvers?


It'd be easy for me to test the 'crushing' question by merely doing my suaul compression, and then pulling out the Bullet and emptying tyhe Cartridge onto some white Paper and spreading the Powder out.


I do know that after being compressed into a Cartridge Case, the Powder is a sort of weak 'solid' which will not spill out or pour out unless the case is banged against the Loading Table a few times with a finger tip covering the Cartridge...and even then, one can pour out some, bang it again, pour out some more, bang it again, pur out the rest.

So it does sort of acheive a weak porous 'solid' of sorts when compressed well.

 

[mykeal]

My only personal experience with 4f is as a flintlock primer. I know of nobody who has successfully used it as a main charge in any application, including short cartridges. It's been around for a very long time, so I would imagine that, if it were any advantage in any specific operation save priming a flintlock, it would be used in that application. And priming flintlocks is the only application where it's universally used today. There's a whole lotta folks gone there before us.