I made a statement at the ArmaLite forum that everything else being equal a heavier bullet will fly farther than a lighter bullet.  My logic was that the Kenetic Energy is equal to 1/2 the mass times the velocity squared.  Therefore the bullet with the greater mass would penetrate more medium (air or what ever) if the velocities and Ballistic Coeficients were the same.

Well, I went to the Sierre Reloding manual to get some proof. I chose the .284, 168 grn. MK vs. the .308 180 grn. MK because ther BCs are pretty similar.

Well according to the manual there trajectories are dang near identicle.  

What gives?

Don`t have any quick answer. But here`s link that might help. http://www.povn.com/%7E4n6/index.htm#Contents

I'm no balistics expert, that's for sure.

The problem I'm seeing is, if the bullet BCs are nearly identical and the velocities which they are driven at are nearly identical, they are going to exibit nearly identical trajectories.

Remember a BC is in effect a representation of how the bullet "flys" and it's ability to buck wind resistance.  You have equal BCs and equal velocities a bullet of .243caliber and a .440BC should have a similar trajectory as a 40caliber bullet with a .440BC so long as the velocities are similar.

Ofcourse one bullet is going to have a hell of a lot more retained energy down range because it's going to be a much heavier bullet.


When talking about the same caliber, say with a 223Rem and you are pushing a 40grn bullet with something like a .200BC at say 3600fps it sheds it's velocity very quickly as opposed to a long skinny 80grn bullet that has a BC up around .480-.520 and is moving at only 2700fps, at short range the 40grn bullet is flatter but around 400-500yds the 80grn bullet begins to show an advantage.


Two online balistics programs I've found are:
not so complicated
http://www.norma.cc/htm_files/javapagee.htm
and more complicated
http://www.cybermesa.com/~jbm/ballistics/traj/traj.html

If they have the same ballistic coefficients, the bullet with the higher velocity will fly farther regardless of mass.

Shoot a slow bullet out of the muzzle of a gun right next to muzzle of a gun out of which you shoot a fast bullet and drop a third bullet straight down from the same height at the same instant the other two guns discharge, all three will hit the ground at the same instant.  The faster bullet will simply have gone farther in the elapsed time. And it does not make any difference if you are dropping a BB while shooting a .22 short and a 155mm. (This assumes flat terrain, barrels parallel to the surface, no wind, etc., etc.)

I understand that, but part of my statement was everthing else being equal.  Distance traveled is a function of velocity and how fast a projectile "scrubs off" its velocity is a fuction of it's BC.  I think the error I was making was in assuming that the K.E. was related to penetration, hence the heavier projectile would penetrate more (air).  Not necessarily so.  

Also the BCs published are for air and might not hold true for anything else.

Well folks, i hate to roll a stone into the garden, but BC's change with range. BC is not(nor was it ever intended) to be a constant. BC IS a measure of "Q", if the distance is defined. Some rather famous bullets have spactacular BC's at three hundred yards but are, comparitivly, enemic at eight hundred yards. Remember, BC is a "curve fitting" or heuristic function and not well supported by some, easily defined, rigourous, law of physics.  

Actually you mean velocity don't you.

Thanks Ugly.

Those links you posted make for some great learning.

peregrine, yeah Sierra gives a BC for different working velocities of their bullets.  A think I remember that the BC of a bullet actually improves as it scrubs off speed during flight, at 3200fps a bullet might do .490 but as it slows down at around 2800 the BC might improve to .510 and get better until some funky stuff happens around the trans-sonic and sub-sonic ranges.

I also think I remember Sierra stating they derive their BCs through several different methods, both at the muzzle and at different points down range.

It's an interesting read to get a Sierra manual and start reading through the part on balistics.  Only the most basic stuff tends to stay in my head, any of the more complex stuff I've got to open it up and look it over.