humm interesting , so if I have a Crony I can estimate the exact presure my load produce ?
Definitely not.
The velocity produced is a pretty close function of the *average* pressure applied to the bullet.
But it isn't average pressure that blows up a gun, *peak* pressure does; and peak pressure doesn't show up particularly well in measured velocities.
A chronograph's combined with a loading manual though, can be sensibly interpreted to get a handle on what is going on. It's no substitute for a pressure measuring apparatus, but those aren't necessary unless you are doing pretty original load development work.
A chronograph is one of the most useful measuring tools you can use for making ammunition. After a powder measuring scale and a set of calipers, a chrono is probably the next most important thing to get.
how does the math formula work ?
Caliber , bullet weight , Bullet speed and powder use ?
Quickload is an "internal ballistics" calculator, that is, it models what happens to the bullet inside the barrel. ("exterior ballistics" is the flight through the air, "terminal ballistics" is the impact with the target).
Interior ballistics programs use a model of the system, typically this sort of thing:
- the rate at which the powder produces gas (typically a function of pressure, temperature, and fraction-of-powder-burnt)
- the rate at which the bullet accelerates (bore area, perhaps a friction model)
These two items are tied together, which gives a differential equation. This is integrated (usually numerically), which gives a prediction of the pressure, temperature, time, bullet position velocity and acceleration. This simulation is run until the bullet leaves the barrel.
Simulated parameters of interest are typically peak pressure produced, average pressure, and muzzle velocity. Some of these outputs are fairly sensitive to initial assumptions, hence the cautions about Quickload (and any other interior ballistics program too) being a useful arrow in the quiver if used as a guideline or development tool, but *NOT* at all a substitute for actual pressure testing.
