I have always wondered how long it took BCG expansion chamber pressure to rise after the bullet passed the gas port, and how long it took to fall after the bullet exited the muzzle. I didn't expect much latency at all.
This paper
Aberdeen paper - WMWerner
shows the BCG expansion chamber pressure (which they call the "pressure at the carrier cavity") rising over a period of about .6 millisecond, and falling over 2 ms (see page 29). This is quite a surprise, as we know that dwell time for an m16a1 (which is what they are using) is only about .2 ms.
The same kind of plot appears on page 23, but the pressure axis is off by a factor of ten. The paper is not very well written. They say that t=0 is the muzzle exit time (which they call the "shot ejection time"), but BCG pressure doesn't start to rise until *after* t=0.
Anyway, if these measurements are correct, a serious rethinking is in order.
By the way, the max BCG velocity of about 15 ft/sec given on page 22 is in close accordance with other measurements I have seen, and also with my own modeling.
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