The effect of a powder chamber on VELOCITY

[Cat Whisperer]

If you read through the article on handgonne's:

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

you will find, right after the use of the ballistic pendulum, a few paragraphs on the effect of increasing velocity that the addition of a powder chamber makes.

I'd always figured that it was only to increase the strength around the powder - added benefits of greater velocity!

[Will Bison]

That was interesting reading. It's hard to argue with empirical testing. If I were to hazard a casual guess, I would have gone with the full bore tube as producing a higher velocity. My rationale would have been that the expanding gas has a greater distance to act upon the projectile. Live and learn.

Also of interest that someone actually still uses a ballistic pendulum. The last one I saw was the one I built in 1964.

Thanks for the interesting link Tim.

[jeeper1]

I have been aware of how much a powder chamber helps for quite some time. Look at the distance differences between a 37mm launcher and a 40mm launcher. The powder chamber is worth 4 times the distance.

[Cat Whisperer]

I have been aware of how much a powder chamber helps for quite some time. Look at the distance differences between a 37mm launcher and a 40mm launcher. The powder chamber is worth 4 times the distance.

Interesting!  (and here I'll show my ignorance, which is which?)  I assume you're talking M79/M203 vs civilian version & the powder chamber would be in the shell casing.

[jeeper1]

Yep.
 The 40mm is mostly military usage and the 37mm is mostly civilian usage.
The 37mm cases have 3 basic designs for the inside of the bases from flat to concave.
The 40mm's have two common designs.
One is a spherical hollow  with several vent holes at an angle.
The other uses a 38 blank cartridge with several variations of vent hole layouts. Both are high pressure chambers which vent the burning gasses to a low pressure chamber to push the projectile out the barrel.
The 37mm will launch a projectile little more than 100 yds. The 40mm will easily go more than 400 yds with the same weight projectile.

[Cat Whisperer]

jeeper1 -

Thanks, that adds a another bit to our storehouse of knowledge.

[jeeper1]

If you want pictures that show the differences then email me at  rlachance@earthlink.net  since some of the pictures are copyrighted.

[Cat Whisperer]

If you want pictures that show the differences then email me at  rlachance@earthlink.net  since some of the pictures are copyrighted.

Thanks for the offer!  I do recall looking into a few of the empties (back in 1972 or so) and seeing the raised area in the middle of the case - didn't attach it to the idea of a powder chamber until now.