Pellet weight / speed ratio ?

[Joeryan]

At the risk of sounding too anal.. lol,  is there a formula to calculate speed based on pellet weight ?  For instance, a 10.65gr dome at 810fps compared to a 10.34gr. Power platform and pellet design being the same ? Or are there too many other variables ?

[DavidS]

At the risk of sounding too anal.. lol,  is there a formula to calculate speed based on pellet weight ?  For instance, a 10.65gr dome at 810fps compared to a 10.34gr. Power platform and pellet design being the same ? Or are there too many other variables ?

You could get somewhat close if you know the MV for a given pellet of a given weight.   That is assuming the same head diameter, approximately the same hardness of lead, etc.

Though you would only get an approximation with out figuring in all of the variables, and in some cases it may be significantly off.

Though usually the biggest issues are going to be the accuracy of the pellet out of your rifle and the ME (muzzle energy).   Generally speaking a heavier pellet will provide greater ME even though the MV (Muzzle velocity) will be a bit lower.     It is the energy that counts when hunting.   And heavier pellets generally carry more energy to the target.

[Bent]

Chairgun gives the answer when you change the pelletweight.. However it also depends how your gun is tuned.
Rsterne has a thread somewhere with his spreadsheets of mindblowing facts, can't seem to find it right now....
But I think one of the graphs was pelletweight/pressure/FPE combined..

[Bwalton]

At the risk of sounding too anal.. lol,  is there a formula to calculate speed based on pellet weight ?  For instance, a 10.65gr dome at 810fps compared to a 10.34gr. Power platform and pellet design being the same ? Or are there too many other variables ?

You have the speed, do you mean energy?ftlb?

[Joeryan]

I know the speed of the 10.65 h&n dome= 809 avg.  But I shot some JSB 10.34 domes ( both 4.52 head size) but, the JSB's seemed noticeably faster. Don't have a chrony here. That was the basis of the post.

[rsterne]

Pellets of the same weight can have different velocities because of the diameter and hardness of the lead.... However, in general terms, if you calculate the FPE for one pellet, the second will have a velocity to give it the same FPE, that's what ChairGun does.... The velocity varies inversely with the square root of the ratio of pellet weights (to keep the FPE constant)....

Bob

[Joeryan]

Ok, Bob, that seems to make sense. 15.49fpe runs about 822 fps. So, the JSB's run 13fps faster.. According to chairgun.

[DOKF]

All things being equal, both momentum (mv) and energy (1/2 mv²) should be constant from pellet to pellet.  However, different pellets will experience differing degrees of drag down the barrel, and different power plants will have differing efficiencies of energy transfer.

The energy and momentum formulae can be used as a guideline approximations, but actual results may vary considerably.