Ballistic Calculator – Bullet Energy, Velocity and Drop

Energy (ft-lb) = weight (gr) × velocity² ÷ 450,240

The constant is two times gravity times the 7,000 grains in a pound, folded into one number — kinetic energy, ½mv², in shooter-friendly units.

The energy on this page. A 150-grain bullet at 2,800 fps: 150 × 2,800² = 1,176,000,000, divided by 450,240 gives 2,611.9 ft-lb at the muzzle. Energy falls with the square of velocity, so it drains away much faster than speed does — by 500 yd the default bullet has shed 61 of its energy but only 37 of its speed, and still carries 1,028 ft-lb.

How drag is applied. Drag is the G1 model: a standard reference bullet’s drag curve, scaled by your bullet’s ballistic coefficient. The deceleration at any moment is C_D(Mach) × velocity² × 0.000208551 ÷ BC, in feet per second squared. For the default bullet leaving at Mach 2.51, the table’s C_D is about 0.539, so the air starts by braking it at roughly 2,215 ft/s² — about 69 times gravity — and eases off as speed falls. The page advances the bullet one foot at a time, re-reading the drag curve at each step, all the way to the end of the table.

Drop, done properly. Gravity pulls at 32.174 ft/s² for the whole flight, and drag acts along the flight path — so once the bullet noses downward, a slice of that drag pushes back up the slope. That is why the true fall is a little kinder than the schoolbook formula: at 500 yd the default bullet has fallen 76 in below the line of the bore, where a plain ½gt² with the same flight time would say about 89 in. Solvers and this page agree; the shortcut does not.

From drop to path. Nobody aims along the bore. Your sight sits 1.5 in above it and your zero tilts the flight so the bullet crosses the line of sight exactly at 100 yd. Path is the bullet’s height against that line: −1.5 in at the muzzle, 0 at the zero, and −58.5 in by 500 yd. That is the number a holdover or a turret click has to cancel.

How the numbers are rounded. Velocities and energies are rounded to whole numbers, path to a tenth of an inch and flight time to the thousandth of a second. Inside the steps nothing is rounded at all — the rounding you see is display only.

The default flight — a 150-grain bullet at 2,800 fps with a G1 ballistic coefficient of 0.398, sight height 1.5 in, zeroed at 100 yd — arrives at 500 yd at 1,756 fps with 1,028 ft-lb of energy, a path of −58.5 in and a flight time of 0.677 s. Every figure in this section was produced by changing the stated field on this page and reading the result back. Each variation changes one input only, so each difference is that input’s own effect, isolated.

A heavier bullet, same speed. Raising the weight to 180 grains, with velocity and BC untouched, lifts muzzle energy from 2,611.9 ft-lb to 3,134.3 ft-lb — exactly the weight ratio, 180 over 150, because energy is proportional to weight at fixed velocity (180 × 2,800² ÷ 450,240 = 3,134.3). At 500 yd the heavier bullet still carries 1,233 ft-lb, against 1,028 ft-lb for the default, and the retained fraction is the same 39% in both cases: with the same BC and the same starting speed, drag treats both bullets alike, so the heavier one simply starts with more and keeps the same share of it. The real-world caution is that heavier bullets rarely keep the same velocity and BC — a real 180-grain load leaves slower, and often sleeker — so this comparison isolates weight’s arithmetic, not a catalogue choice. When you compare two real loads, change all three of weight, velocity and BC together, or you will credit weight with what velocity actually did.

A slower start. Dropping muzzle velocity to 2,600 fps, with weight and BC untouched, cuts muzzle energy from 2,611.9 ft-lb to 2,252.1 ft-lb — a 13.8% loss of energy from a 7.1% loss of speed, because energy follows the square of velocity (150 × 2,600² ÷ 450,240 = 2,252.1). At 500 yd the slower bullet retains 860 ft-lb, or 38% of its muzzle figure, against the default’s 1,028 ft-lb and 39%. Two lessons hide in that small gap. First, the slower bullet loses slightly more of its energy proportionally, because it spends longer in the air being dragged. Second, and more important for shooting, velocity is the input most likely to be wrong in real life: two rifles chambered alike can disagree by 50 fps or more, and the base page’s truing advice — adjust the velocity first when impacts disagree with the table — follows directly from how much leverage velocity has over every downrange number.

A sleeker bullet. Raising the BC from 0.398 to 0.500, with weight and velocity untouched, leaves muzzle energy exactly where it was at 2,611.9 ft-lb — the BC never enters the muzzle-energy formula — but transforms the far end: at 500 yd the sleeker bullet is still travelling at 1,946 fps (against 1,756 fps), carries 1,262 ft-lb (against 1,028 ft-lb, or 48% retained against 39%), sits at a path of −53.4 in (against −58.5 in) and arrives sooner, in 0.643 s against 0.677 s. That is the whole argument for sleek bullets in one comparison: the same launch, but less speed lost, less energy lost, less drop to correct and less time for wind to work on — though this page models no wind, so the last benefit is one you must take from a full solver. It is also why a published BC deserves scepticism in both directions: it is an average over a speed band, and as the bullet slows through the speed of sound its true drag match to the G1 curve shifts, most of all for modern boat-tails.

A farther zero. Moving the zero from 100 yd to 200 yd changes nothing about the bullet’s flight through the air and everything about how you read it: at 500 yd the velocity is still 1,756 fps, the energy still 1,028 ft-lb and the flight time still 0.677 s, but the path improves from −58.5 in to −49.1 in, because the line of sight is now tilted to meet the bullet farther out. That 9.4-inch difference is not a flatter trajectory — it is a different ruler. The zero describes your rifle, not your bullet, and choosing it is a trade: a farther zero buys a smaller correction at long range and pays for it with a higher mid-range arc, the bullet rising above the line of sight between muzzle and zero. Never compare two path figures struck from different zeros as if they described different bullets.

Each row changes one input from the default (150 gr, 2,800 fps, BC 0.398, zero 100 yd) and reports the 500 yd figures.

Dashes mark figures not cited for that row, not figures that did not change: the weight and velocity rows were verified on muzzle energy and 500 yd energy, the figures that carry those rows’ arguments. The pattern to carry away is which column each input moves. Weight moves the energy column. Velocity moves every column, through the square law. BC moves everything downrange but nothing at the muzzle. Zero moves only the path column. A table that disagrees with your targets can usually be diagnosed by which column is wrong — and that diagnosis tells you which input to true first.

Start with the shape, not the far end. The default table’s path column tells a story that the 500 yd figure alone cannot: −1.5 in at the muzzle, −0.1 in at 50 yd, exactly 0.0 at the 100 yd zero, then −1.2 in at 150 yd, −3.8 in at 200 yd, −8.0 in at 250 yd, −13.9 in at 300 yd, −21.7 in at 350 yd, −31.6 in at 400 yd, −43.8 in at 450 yd and −58.5 in at 500 yd. The growth accelerates because the bullet is both falling and slowing: each successive 50 yd costs more drop than the one before. For holdover purposes, the useful numbers are the near ones — inside 200 yd the correction is under 4 inches, which many rifles can absorb inside ordinary aiming error, while beyond 300 yd the correction grows by roughly 8 to 15 inches per 50 yd and must be dialled or held deliberately. A shooter who only memorises the 500 yd figure will overcorrect near and undercorrect far.

Drop is not path, and the difference is the sight. The base page puts the default bullet’s true fall at 500 yd at 76 in below the line of the bore, against a path of −58.5 in below the line of sight. The 17.5-inch gap between those two numbers is the sight height and the zero tilt doing their work: the sight sits 1.5 in above the bore, and the flight is tilted so the bullet crosses the line of sight at 100 yd. Holdovers and turret clicks correct path, never drop, because path is measured from the line you actually aim along. The schoolbook shortcut — plain ½gt² with the same 0.677 s flight time, which would say about 89 in — overstates even the drop, because drag acts along the flight path and, once the bullet noses downward, a slice of that drag pushes back up the slope. Three numbers, three meanings: 89 in is the shortcut, 76 in is the drop, −58.5 in is the correction you actually apply.

Energy and speed tell different stories at distance. By 500 yd the default bullet has given up 37% of its speed but 61% of its energy, and that asymmetry is the square law again: energy falls with velocity squared, so every increment of speed lost costs more energy than the last. For judging what a bullet can still do downrange, energy is the figure that matters, and its faster decay is why a load that looks adequate at the muzzle can look thin at 500 yd. The velocity column matters differently: it governs flight time (0.677 s here), and flight time governs how long wind, gravity and your own wobble have to act. A table read for energy alone will flatter a slow, heavy bullet; a table read for velocity alone will flatter a fast, light one. Read both columns, and let the intended distance decide which one rules.

True the table before trusting it. The base page’s method is the right one and bears repeating in full: chronograph the load in your own rifle, run the table on that measured velocity, then shoot groups at real distances and compare the centres. If the bullet lands consistently high or low, adjust the velocity you feed the model first — it is the input most likely to be off, since published velocities come from someone else’s barrel, powder lot and weather — and only then nudge the BC. Altitude is the next suspect: the air at a mile of altitude is roughly a fifth thinner than the standard sea-level air assumed here, and thin air flies flatter, so a table trued at sea level will shoot high in the mountains. Done once, carefully, the trued table holds up across conditions far better than any out-of-the-box figure, this page’s included.

Know what is missing before the shot that matters. This page models drag, gravity and your zero in still, standard sea-level air at 59°F. It does not model wind — the biggest omission of all, with a steady 10 mph crosswind moving the .308 load roughly 34 inches sideways at 500 yd according to full solvers, more than many drop corrections — nor spin drift, Coriolis, cant, or the shift in true drag as a bullet slows through the speed of sound. Use this page for the vertical story, and a full solver plus your own shooting for the rest. And this page contains no loading or handloading data and no advice on making ammunition: for that, use the ammunition and powder manufacturers’ published manuals and follow them exactly. A trajectory table, however well trued, is not a load manual.