MyLoads is an internal ballistics calculator and simulator. You give it a cartridge, bullet, powder, charge, and barrel length, and it estimates the muzzle velocity and a chamber-pressure interval, then flags loads that look unsafe. Those numbers are estimates from a physics model — useful for building intuition and comparing options, but they can be wrong, and they are never a substitute for current published load data. Always cross-check a current loading manual before loading anything.
Estimate a load — pick a cartridge, bullet, powder, and charge, then press Simulate to see the muzzle velocity and a low–nominal–high pressure interval, with safety flags.
Compare options — open the charge ladder to see how velocity and pressure move as the charge changes, or use the reverse powder search to compare powders for the same load.
Keep your work — saved loads, recent loads, shareable links, and a printable load sheet all work right in your browser.
Your first simulation
MyLoads opens on a sample .308 Winchester load, so you can see how it works in a few clicks:
Press Simulate.
Read the results — the muzzle velocity, and the pressure shown as a low–nominal–high interval (never a single number, because real pressure has spread). Note any safety flags.
Change something — nudge the charge, or pick a different bullet or powder — and press Simulate again to see the effect.
Open the charge ladder to see velocity and pressure across a range of charges at once.
The first time you simulate a given load, MyLoads asks you to confirm you have cross-checked it against published data. That prompt is for your safety, not a formality.
How the inputs change pressure and velocity
Use these to build intuition for what each input does — then confirm against published data, because the safe range depends on your exact components:
Powder charge — the biggest lever. More powder makes more gas, so both pressure and velocity rise — but near the top, pressure climbs faster than velocity, so a small extra charge can spike pressure a lot. That is why you work up in small steps.
Bullet weight — a heavier bullet resists acceleration and stays in the bore longer, so for the same charge it builds higher peak pressure but usually gives lower muzzle velocity; a lighter bullet is the opposite. Changing bullet weight changes the safe charge window — a charge that is fine under a light bullet can be over-pressure under a heavy one.
Bullet shape & construction — a longer bearing surface or a harder jacket grips the bore more, nudging pressure up. The ogive and boat-tail mostly affect flight downrange (drag) rather than chamber pressure, but they interact with how deep the bullet seats.
Seating depth / COAL — seating the bullet deeper (a shorter overall length) leaves less room for the burning powder, which raises pressure for the same charge; seating it longer lowers pressure but can run into the rifling. MyLoads shows the COAL it used — use the published COAL for your bullet.
Barrel length — a longer barrel gives the gases more time to push the bullet, so velocity rises (with diminishing returns); it barely changes peak pressure, which happens early, near the chamber.
Charge temperature — many powders burn faster when warm, raising pressure and velocity, so a load worked up on a cold day can run hotter in summer heat.
Using MyLoads without an account
You can do all of that without signing in. The calculator runs entirely in your browser, and anything you save without an account stays on your device — nothing is sent to us. Saved loads, recent loads, unit and layout preferences, share links, and PDF printing are all available signed-out.
What a free account adds (optional)
Signing up is optional and free during the early-release period. It unlocks the features that have to be tied to you and kept in sync:
Per-rifle calibration — import your chronograph data and MyLoads tunes the model to your rifle, so the estimates match what your barrel actually does. This is the single biggest accuracy upgrade.
Rifles & chronograph history — keep a profile for each rifle and the velocity data you have measured — and the group each string shot, in MOA, so your accuracy history lives right next to your velocities.
Your rifle & load library — one place that lists every rifle next to the loads you have worked up in it, each showing the median group size you have recorded for it — so the load that shoots tightest in each rifle is easy to spot. Tap a load to open it back in the workbench.
Cross-device cloud sync — your loads, rifles, and calibration follow you to your other devices.
Loading safely
MyLoads is a screening and learning tool, not a loading manual. Whatever it shows, follow the basics every published source agrees on:
Treat every number as an estimate. A clean result is not a green light — it is one data point from a model that can be wrong.
Start low and work up. Begin at a published start charge from a current manual or the powder or bullet maker, and increase in small steps, checking your rifle and your cases at each step.
Never exceed the published maximum charge for your exact components, even if MyLoads shows headroom.
Re-check after any change. Swapping bullet, powder (or even powder lot), primer, brass, or seating depth changes pressure — verify the new combination against published data.
Watch for real pressure signs MyLoads cannot see — stiff bolt lift, flattened or cratered primers, ejector marks, or case-head expansion. If you see them, stop and back off.
When in doubt, ask. A current loading manual and an experienced reloader are the authority; MyLoads is not a substitute for either.
Keep reading: getting the most from your rifle
New to this? Everything above is enough to get going with MyLoads. When you want to chase precision, here is what load development is really about — accuracy nodes, the brass itself, and an honest word on what a simulator can and cannot tell you.
What an accuracy node is
Reloaders talk about accuracy nodes (or sweet spots): a charge weight — and a bullet seating depth — where a particular rifle groups tightest and is least sensitive to tiny changes. The idea is that inside a node a tenth of a grain either way barely moves your point of impact, so the load is forgiving and repeatable. A node belongs to your specific rifle, barrel, and components together — it is not something any calculator can predict for you.
How reloaders look for them
Finding a node is range work, done safely within the published start-to-max charge range:
Charge ladder — load a series stepping the charge up in small increments from the published start toward (never past) max, fire them, and look for a stretch where the group center — or the chronograph velocity — stops moving: a flat spot. MyLoads’ charge ladder helps you plan that test and shows the predicted velocity and pressure trend, but the node itself is found on paper, at the range.
Seating-depth test — once a charge looks promising, vary how far the bullet sits off the rifling in small steps and look for the depth that tightens groups; seating depth often matters as much as charge.
Chronograph numbers — a low spread in velocity (small extreme spread and standard deviation) is a sign of a consistent load. Feed that chronograph data into MyLoads’ per-rifle calibration and its velocity estimates start matching your barrel, so your next ladder begins closer to the mark and wastes fewer components.
Recording your groups — alongside the velocities, log the group each string actually printed — type the size in MOA, or enter the group measurement and the distance and MyLoads works out the MOA for you. It records what you measured rather than predicting anything, and keeps the median group for each load, so across a season you can see which load your rifle truly shoots tightest; the library gathers it all per rifle.
Brass: case capacity and consistency
Your brass is part of the load. A case’s internal volume — its capacity — is one of the numbers the engine uses, and real cases vary in ways a nominal value cannot capture:
Capacity varies by maker — different brands of brass for the same cartridge have different internal volume (wall and web thickness differ). A smaller-capacity case raises pressure and velocity for the same charge, so switching brass brands is a real component change — back the charge off and work it up again rather than carrying the old charge over.
Fired vs unfired — capacity is not fixed. New brass, once-fired brass sized back down, and brass fired many times all differ — a case fired in your chamber and not yet resized holds a little more than a full-length-sized one, and brass flows and thickens with use. Keep your prep (sizing, trim length, annealing) consistent so the capacity you load into stays consistent.
Consistency drives accuracy — case-to-case capacity spread shows up as velocity spread (extreme spread and standard deviation), which becomes vertical dispersion at distance. Uniform, quality brass — sorted by weight or capacity, with uniform necks and prep — is often a bigger precision gain than chasing the last node.
Measuring it yourself (grains of water) — plug the flash hole first — a spent (fired) primer left in the pocket works well — then weigh the case empty, fill it level to the case mouth with water, and weigh again; the difference in grains is its water capacity in grains of water (grains H₂O). Plug before the empty weighing, not after: that way the plug sits on the scale for both weighings and its own weight cancels out instead of counting as water. Use a fired, not-yet-resized case — that is the volume the powder actually burns in — and compare brands and lots the same way; a few grains of water is a real pressure and velocity difference.
What MyLoads assumes — it works from a nominal case capacity for each cartridge, so the numbers assume average brass; yours may sit higher or lower. Once you have measured yours (above), the load editor has an optional case-capacity field — enter your grains of water and MyLoads uses it instead of the nominal, within a sensible range of it. Either way the result is still an estimate, which is also why per-rifle calibration is worth it: fitting to the velocities your setup actually produces quietly absorbs your brass, chamber, and barrel together.
Seating depth: COAL, the lands, and your magazine
How far you seat the bullet sets both pressure (above) and how far it jumps before it meets the rifling. Three numbers worth measuring:
Measuring COAL — cartridge overall length is the loaded round measured tip-to-base with calipers. Because bullet tips vary, careful measurements use a bullet comparator that gauges off the ogive instead of the soft tip. MyLoads has an optional COAL field — enter yours and it uses that geometry; leave it blank and it estimates a COAL from the cartridge and bullet.
Finding the lands — the point where the bullet first touches the rifling sets your jump. Common ways to find it are a chamber OAL gauge (it eases a bullet up to the lands in a modified case) or the split-neck method (a lightly-gripping fired case you seat a bullet in long, chamber gently, then measure where the lands pushed it back). Seating at or into the lands raises pressure sharply, so treat any load near them as a fresh work-up from a reduced charge.
Maximum magazine length — whatever COAL you pick has to feed. Measure the longest round your magazine accepts and stay under it for a repeater; a longer round that only single-feeds is fine for load development but not for shooting from the magazine.
How the pressure number is simulated (and why seating may not move it)
For each cartridge, MyLoads runs its pressure simulation on the same case-volume basis its powder models were validated against published data with — for many bottleneck rifle cartridges that is the powder space under the seated bullet, while for many deep-seated, straight-wall, and handgun cartridges the validated basis is the full case volume. Two honest consequences:
The fill ratio is always physical — whatever basis the pressure runs on, the fill percentage shown is the real powder fill of the seated case — a compressed load reads compressed, a half-empty case reads half empty.
On some cartridges seating depth changes the fill, not the predicted pressure — when a cartridge simulates on the full-case basis, seating the bullet deeper (a shorter COAL) will not raise the predicted pressure the way it does in a real chamber — the result panel says so on exactly those cartridges. Real deep seating DOES raise real pressure, sometimes sharply, so treat seating changes on such a cartridge as untested by the calculator: work from a current published manual and back the charge off when you seat deeper. This is a stated limit of the model, not something to tune around.
Sample size
Be skeptical of nodes found with tiny samples. A small group of three or five shots is easily produced by ordinary shot-to-shot scatter and can disappear over fifty rounds. Many precision shooters now treat a lot of apparent nodes as small-sample noise and put their trust in larger sample sizes. Shoot multiple groups, and focus on low extreme spread and standard deviation, good brass, and seating depth. Use a ladder to narrow the search, then confirm a promising load with a larger group before you rely on it. Remember what MyLoads is: it estimates internal ballistics — pressure and velocity — and it cannot tell you how your rifle will group. Only shooting can do that. It can keep a record of the groups you do shoot and show the stats for each load, but that is your measured result, not a prediction.