Derringer barrel length

[Derringeer]

Hello. I’m about to make a very small black powder derringer in cal .41, Philly style. I want to make the barrel very short, and I read that derringer-barrels could be as short as 1.5” back in the days. But such a barrel will lose alot velocity, especially with black powder that burns relatively slow.

How much velocity losses will a too short barrel generate step by step? For example, will a 2.5” barrel make a big difference compared to a 3”?

Is there any optimal barrel length in order to keep it as short as possible but without too much velocity loss? What was the most common barrel length of BP-derringers back in the days?

 

[Hawg]

You're not going to be able to get enough 4F into a 2.5 inch barrel to get much velocity to start with. Going to 3 inches isn't going to be much of an improvement. With barrels that short most of your powder is going to be muzzle flash. The gun That killed Lincoln had a 2.5 inch barrel, was fired point blank and didn't leave an exit wound.

 

[Derringeer]

If the total length of the barrel is 4”, and it’s chambered in .40 cal loaded with a roundball, what’s the maximum charge suitable for the caliber regarding the length of the barrel? I read something about 25 grains of black gunpowder, more than that and it will only generate a bigger muzzle flash, but I believe the barrel was longer than 4” in that case.

If the barrel is short, can the velocity turn out higher with a smaller charge than a big charge, because with a smaller charge the ball will be chambered more deeply inside of the bore and therefore travelling a longer distance inside of the bore?

I’ll use Pyrodex P FFFG btw.

 

[Hawg]

With a barrel that short you're not going to see much velocity change. With a rifle barrel people talk about the optimal load where all the powder is burned inside the barrel but you can go over that and still get an increase in velocity. However it is a case of diminishing returns. There comes a point where velocity does not increase with an increase in powder. I would think 15 grains would be a more reasonable load.

 

[Derringeer]

https://www.theboxotruth.com/educational-zone-66-shooting-a-black-powder-pistol/

Well, this is weird. A philadelphia derringer with a 3” barrel penetrated only one jug of water when loaded with 30 grains of black powder. But when loaded with 40 grains of black powder, it penetrated 4 jugs.

 

[denster]

Go back and re read the article. The 40gr charge was in a long barreled kentucky style pistol.

 

[jaguarxk120]

The 40 grain charge was also used in the derringer and went through 4 jugs!

 

[denster]

Yep so it was didn't read to the end.