Physics, blackpowder ballistics and 1399

[Salkehatchie]

The internet is a great tool.

Found this, and thought it might be interesting to you guys.

http://www.musketeer.ch/blackpowder/handgonne.html

[northmn]

You really cannot compare modern powder to the earliest stuff.  Prince Rupert was said to have improved the existing black powder and make it 10 times stronger than the stuff before hand.  This was in the late part of the 1600's.  10 grains of Rupert's improved powder equalled 100 grains of the previous?   The claims on the earliest "gonnes" and their ineffectiveness may have had some foundation.

DP

[Fred_Dwyer]

Interesting stuff.
I rather think the mouth as a touch-hole sort of a "cute" touch.

OK, so I will break the rules here and compare to cartridges. In cartridges it is seen that in bottle-neck cartridges that the efficiency goes down, that velocity per grain is lower than a straight cartridge. Yeah you can get higher velocities with a bottleneck cartridge but compared to the same caliber and powder charge in a straight cartridge the velocity will be lower than an insanely long straight cartridge. The simplistic explanation I got was that the expanding gases need to funnel through the bottleneck so loses some propelling force compared to a straight sided cartridge.
So again looking at the simplistic explanation, the smaller powder chamber then would do the inverse and be more efficient than a bottleneck since it is the exact opposite.
Makes sense from that view.

OK, but looking at the fluid dynamics of the system; let's think hydraulics.
You put a bottle jack under your truck and with a few foot pounds of pressure on the handle your are easily lifting a 2 ton truck. Small cylinder to larger cylinder hydraulic advantage.

[heelerau]

I made some black powder using Ulrich Bretchers  reciepe, unfortunately only had charcoal from a cherry tree. The stuff went off in a colt navy fine but only a third of the strength of commercial black. Tried it out in the Lancaster had to use commercial black for priming, went off ok, but no guts. Have got some willow to make charcoal, and will get a small ball mill and a bunch of brass balls to give a better mixing. It is a really interesting website.

Cheers

Gordon

[Paul Griffith]

So again looking at the simplistic explanation, the smaller powder chamber then would do the inverse and be more efficient than a bottleneck since it is the exact opposite.

Along this train of thought. We did some work one time comparing a flat bottom breech to a cone shaped breech simular to one in a Manton flint shotgun. With the same barrel, same charge,ect. we picked up a little over 10% muzzle velocity with the cone.  Now, in a way we did lengthen the barrel the length of the cone in the bottom & this would add a bit of velocity. The benifit of shaping the charge has been known for quite some time. I think it was Joe Manton back in the early 1800s who made up some sabot type giz-whiz for cannon that he felt increased carry of the projectile.

[Fred_Dwyer]

With the conical breach that was ignited at the mouth, that easily would have a shaped-charge effect. I don't think it would lengthen the barrel to effect a measurable velocity change.

I've seen the reduced tube powder chamber before in drawings and pictures of really old mortars. I've been googling a whole lot of cannon and mortar pictures but haven't come up with a picture to share that depicts this chamber set up. I guess way back when they had figured out the benefit but opted for ease or speed of construction

[Paul Griffith]

The most radical example of the reduced chamber I've seen was a bowling ball morter that the Bevel Bros. have.  In the bottom of this hole large enough to hold a bowling ball is a small pocket for the powder maybe an inch dia. & something like that deep as I recall.  Did a great job of lobbing a ball out a couple hundred yds or so. Although ocasionally the ball couldn't take the shock & would puke out in a spray of little pieces.

[Fred_Dwyer]

Ah, a little perseverance pays off. Some of the pix show a detachable chamber, some showing the chamber in a reduced diameter from the bore.
http://riv.co.nz/rnza/hist/gun/firstgun.htm