expected velocity

[eph289]

I've been building a 40 cal. percussion rifle. Yesterday I got to the point I needed to shoot it with a temperary rear sight to see what I needed for a permenent one .
I used a PRB with 30 gr.fff goex in a 42 in. barrel . The velocity was 1360 f/s . I thought the velocity would be greater .
Does anyone know what kind of velocities to expect from a 42 and a 36 in. barrel with this load ; as i am intending to shorten it as soon as I get the couage . It did group very well.

 

[Dave Rosenthal]

How tight was the patch? The tighter the patch, the more velocity!

Paul V. and some of the other guys might have a reference chart that you're looking for.

Dave

 

[nchawkeye]

I'd say with a 42 inch barrel you will get about 1360fps and 30 grs FFF powder... :grin:

That's a plenty for what a .40 is made for...I've even gone down to 25 grs for squirrels, it shoots flat out to 50 yards....Mine shoots about 3 inches high at 50 yards with 60grs FFF, but I can't use it for turkeys in NC and I have a .54 for deer, so I stick with 25-40 grains for most of my shooting....

I wouldn't shorten a .40, not unless the barrel is an inch thick or better, mine is 13/16 and it hangs right.

 

[paulvallandigham]

In a .40, using a .390 or .395 ball and .010 to .015 patch, lubed, you can expect to get 1800-2000 fps with 40 grains of FFFg powder. That is at the muzzle. the small, 95 grain ball is going to lose a lot of velocity by the time it reaches 100 yds, and may barely exceed the speed of sound. Use a chronograph. I don't cosider a 36 inch barrel " short " for this caliber of gun. I think you will enjoy shooting those 30 grain, and event he 25 grain loads in that rifle. If you choose to use this rifle to hunt deer, then use the larger powder charge, but keep your shots inside 75 yards if possible.

 

[wszumera]

I've been building a 40 cal. percussion rifle. Yesterday I got to the point I needed to shoot it with a temperary rear sight to see what I needed for a permenent one .

I used a PRB with 30 gr.fff goex in a 42 in. barrel . The velocity was 1360 f/s . I thought the velocity would be greater .

Uncle (Eph289) built himself another underhammer with a lock he made himself and walnut stock he sawed out of a tree. He built the band mill that sawed it.

As soon as his kids are back in school, I'll get to shoot the .62 he built for me with him as his .40 sips powder and lead :wink:

I'll problably get told about how economical his latest rifle is. :grin:

Clutch

 

[CoyoteJoe]

The old Lyman first edition black powder handbook lists a 43" barrel with .395" ball, 30 grains Gerhart-Owen (now Goex) 3f at 1343fps, so you are right there. You'll have about 380 ft.lb. muzzle energy and about 120 ft.lb. remaining at 100 yards. I doubt you'd have any great velocity loss by cutting the barrel to 36" but it sure would spoil the graceful lines of a slim rifle.