As preparation for reverse engineering of the AR18, lets break down what goes on during an AR15 cycle of operations.
>1. When the trigger is pulled, the firing pin is impacted against the bullet primer, and the cartridge gunpowder is ignited. Within the first few inches of bullet travel, the entirety of the gunpowder is burned, and peak chamber/barrel pressure is achieved.
>2. As the barrel travels down the barrel, increasing volume causes pressure to drop.
>3. When the bullet passes the gas port, gas flows into the gas tube under gas flow choking conditions (gas port size). The bullet continues to travel down the bore, and chamber/barrel pressure continues to drop.
>4. Pressure at the expansion chamber in the BCG pushes the bolt forward (counteracting some of the rearward chamber pressure) and the carrier backward. As the carrier retracts, the cam path causes the bolt to rotate out of locking position. Friction of the bolt lugs against the locking surfaces may be relevant.
>5. The bullet leaves the barrel and pressure drops rapidly.
>6. The carrier moves back, the bolt is unlocked, the cartridge is extracted and ejected.
All this occurs along with the influence of mass and springs, and not necessarily strictly in all that order. Load data for .223 cartridges is available.
modeling the gas flow has been difficult, mostly because i dont know what assumptions are reasonable to make given the high pressure / high temperature nature of interior ballistics
i had come up with a number of dynamic and fluid flow equations and after reading the US Army Materiel Command's "Gun Series Automatic Weapons" and they were pretty much right on the money
i've found the powder characteristics for WC844 in Army documentation so i can give estimations for orifice flow (through a gas port) and the pressure curve (as the bullet goes down the barrel)
ok im starting from scratch again this time gonna build it in mathcad, excel just isn't up for this also now im performing my own pressure time simulations using the work layed out in Computational interior ballistics modeling i'll also be doing my own combustion reaction simulations using some NASA software that got illegaly reposted by some pajeets