Things that are acid (like fruit) or sufficiently sweet (like jam) or salty are able to canned in a boiling water bath
Things that have no chemical protection (like meat, many vegetables) need to be canned at high pressure so they boil at well over 100°C and destroy all pathogens
They had live ammo and live shooting non-disabled guns. The crew were using them on the incident day to shoot cans, and this was the armorer's first second film job
Standing alone 'm' is metre.
With a decimal modifier ahead of it, 'm' is metre
Immediately before a symbol it is milli (one thousandth)
mm - the first m is before the metre symbol, it is the milli multiplier, the second m is after a multiplier, so it is the symbol for metre
mHz - the m is before the symbol Hz (for Hertz) so it is the milli multiplier
km - the m is after the K (kilo, thousand times) multiplier, so it is metre
You probably spell metre 'meter', but a meter is a whole different word in English