[Bullet]

Does anyone know how to figure muzzel velocity from loads chronographed at 10 feet. I believe there is a formula for this but if there is I forgot it.

[30Cal]

The difference between 10' and the muzzle is negligible. If you mess around with ballistics tables, try changing the muzzle velocity by 50fps and see what happens to the trajectory (in the ranges where the rifle will likely be used). Virtually nil.

Ty

[1911Tuner]

Just a rough estimate would probably to add 10 fps to your reading.
Estimate taken from Army 7.62 Nato ammo that's tested at 25 meters from
the muzzle at 2750 fps as spec. Actual muzzle velocity for the ammo generally runs to 2800 fps at 25 feet distance from the muzzle...At least
that's been my experience. It won't be exact, but it'll be too close to
make any practical difference.

Luck!

Tuner

[Smokey Joe]

The rule of thumb as I understand it is, to add 1 fps to the measured velocity for each 1 foot the chrono is from the muzzle. That said, I agree with the above posts that the difference is negligible. Any difference of > 50 fps is negligible, IMHO. There are too many other factors involved to worry about cutting fps any finer than that.

[dodgestdshift]

There was an article in the American Rifleman discussing that very question. I put the formula into the ballistic formula program I wrote that I still use. I looked for it in my files, and could not find it.

If you have a computer and a program that will run ballistics stuff, you could play with it. Enter a muzzle velocity about 20 fps higher than your measured velocity, and set the range increment for 3 yards. The velocity difference between 9 feet and 10 feet is neglible. Then keep changing muzzle velocity until the 3 yd velocity is equal to your measured velocity and you have it. I wouldn't want to do this a lot, but for a few times it is feasible.