Ballistics/Physics Questions

[Old Goat]

I am using the Big game info site for ballistics calculations. One thing I dont understand is the energy ft/#. The column labeled "momentum lb ft/s" gives what is mathamitically proportional to the the velocity. If I put in 2800 fps it starts at 100%. If I put in 2900 fps it starts at 103.57%. How can you start with more than 100%? I assumed that the energy would follow the velocity...but if you compare the enery at 500 yards to the energy at the muzzel...it calculates at 53.95% when the velocity is 73.45% If you have a bullet that retains all of its mass over it's flight, would not the energy be proportional to the velocity?

[Hunt'nFish]

it is.....Energy is 1/2MV^2. So it's porpotional to the square of the velocity.

Light bullets tend to loose velocity quicker than heavier bullets. Not because they are lighter, that has nothing to do with it, but rather because they typically have a lower BC.
Hunt'nFish

[StickFish]

Ft#'s isn't really a very valuable number as you've just pointed out. Lots of places on the net discount it as a measure of performance. I stopped looking at it years ago. Velocity are all I car about. Simply put at reasonable hunting ranges - does it really matter? Deliver the bullet on target in the kill zone at reasonable velocity and the rest is meat on the table.

[Big Billy]

Originally Posted by Old Salt

I am using the Big game info site for ballistics calculations. One thing I dont understand is the energy ft/#. The column labeled "momentum lb ft/s" gives what is mathamitically proportional to the the velocity. If I put in 2800 fps it starts at 100%. If I put in 2900 fps it starts at 103.57%. How can you start with more than 100%? I assumed that the energy would follow the velocity...but if you compare the enery at 500 yards to the energy at the muzzel...it calculates at 53.95% when the velocity is 73.45% If you have a bullet that retains all of its mass over it's flight, would not the energy be proportional to the velocity?

what caliber and bullet weight are you working with?

[holyhogmolly]

It's that v squared that kills you. and actually, the weight is what matters while talking about how quickly a round will slow down, it's called inertia, or Newton's first law of motion. The more massive something is, the more it takes to change what that object is doing, meaning a heavy round moving fast will require more energy to slow it down than a light round moving at the same speed. A small change in speed (read velocity) translates to a large change in energy.

[SImudBogger]

Ifish nerd alert!!

[scottishsetter]

????HeHeHeHe****ha!

[baltz526]

short barrel, faster powder, mid weight bullet= best perfomance at resonable range for short barrel 338win mag. long barrel, slow powder, heavy high BC bullet= best perfomance at long range. zero to 400yds, short barrel mid weight bullet. 400yds plus, long barrel, heavy high BC bullet. for all ranges long barrel heavy high BC bullet. if you want a light quick pointing rifle, don't worry about shooting past 400yds

[Old Goat]

Trimming 3" I believe will reduce my velocity about 100 fps. Based on the 2900 fps load, and reducing to 2800 fps...There isnt that much difference in ballistics. 500 yards 4" more bullet drop, 200 fps less velocity, 3 ft# less momentum. This is all academic of course. I am thinking the best of both worlds to a large degree. Plus I would assume a more accurate crown on the muzzel. We will see!