Muzzle velocity, powder and lead

[Twanger]

Frustrated with the infinite number of loads out there, last spring I decided to try to figure out the relationship between muzzle velocity, grains of powder, and bullet weight. I shot a wide variety of loads through a chrony, and got the plots shown above. It turns out to be pretty simple.

MV = 2518 X^(0.344), where X is the number of grains of powder divided by the weight of the bullet in grains. This is the least squares curve fit to the blue data points, also shown in blue.

Now I, and you, can figure out the muzzle velocity of any load just by looking it up on the chart. If your gun has a 22-26" barrel and is between 45 and 50 caliber, this should be very close. I've had many people try it and verify it.

The magenta curve is for a muzzleloading pistol with a 14.5" barrel and T72F powder.

A lengthy article on this by yours truely was published in the March 2005 Sunrise Archery News Letter. See: www.sunrisearchery.com/

The short story is:

Say you want to know what MV you'll get using 100gr T72F powder and a 200gr bullet.
Divide 100 by 200 and you get 0.5 grains of powder per grain of lead.
Now look up what MV you get for 0.5: I.e. Follow the vertical line at 0.500 up to where it hits the blue curve. Now follow that line across to the left and read off the MV. It's 2000 fps.

It's that easy.

There's another way to use this that I really like. Say your ballistics program says you need 1800 fps to keep you happy out to 150 yds. How much powder do you need for that 200gr bullet? Well, just follow the 1800 fps line right until it hits blue curve, and follow that vertically down to find out how many grains of powder you need for each grain of that 200gr bullet. It says you need 0.38 grain of powder per grain of lead. So multiply 0.38 by 200 and you get 76 grain of powder. That's it.

A good companion resource to this is the JBM ballistic calculator, See:
www.eskimo.com/~jbm/calculations/traj_basic/traj_basic.html

The only caveat I should give with using this table is:
DON'T EXCEED YOUR MANUFACTURERS MAX LOAD!

[eshoremd]

uh oh! walts speaking in code again guys! your way too smart.

wouldn't it be all different with a different type powder?

[Twanger]

eshoremd - Hey now, this one's pretty simple.

Yes, it would be different with different powder, but there are simple correction factors. This rule is for Triple 7, 2f. Loose Pyrodex RS is 80% the strength of T72f, so if you use it you need to take the pyrodex volume and multiple by 0.8 before you divide by the bullet weight. T73f is 5% hotter than T72f so you multiply by 1.05 before dividing by the bullet weight. Loose 2f black powder is about the same as pyrodex RS so the correction factor is 0.8 for 'holy' black.

This is also for loose powder only...

Pellets are a little more complicated. 777 pellets are actually made lighter than pyrodex pellets so that they provide about the same muzzle velocity. Actually a tad less in my Encore. For example: I get 1800 fps in my Encore from two "50gr" T7 pellets and 1850 with two pyrodex pellets.

[eshoremd]

i shoot 44.5gr of accurate arms 5744.


how many deer you guys taken so far. i would have really liked to get into that but i hate traveling around 495. road sucks! didnt want to devote myself to something i couldnt regularly be involved with. looks like animal connection has done a really professional job.

[Twanger]

Ahhhhh... the Savage 10ML ... yeah, I havn't done this for smokeless powder yet.
It would be very easy to do so. I just don't yet own the Savage.

The group has taken about 50 deer out of that neighborhood so far.
We're walking new properties every week. The homeowners are for the most-part desperate to get rid of these deer. Any ornamental bush that doesn't have a guard or net around it is toast. Many homes have 10-foot fences around the property. They are having a hard time of it. Word is that they are already seeing fewer deer.