Does being firearms knowledgeable take enjoyment out of things?
Er, let me fix that for you: remove the word "firearms."
Gravity was a great movie, but, an utter fantasy. Gravity does not, neither does orbital mechanics work the way it's shown in the movie. Ricochets do not gain momentum. Weightlessness does not equal masslessness.
Once you suspend that belief, then you can gloss over how an MD is able to suss out Soviet space equipment and operation of same; or that PRC space vehicles would be exact copies of Soviet ones.
Torches in movies used as flashlights. Ever try that? Put the super-bright pupil-contracting light in front of you to see out into absolute darkness? If you ever need to do this, you want it above your head or out to the side; over your head is like to drip burning combustion products on your flammable hair, though.
Aircraft fuel specified in gallons instead of by weight.
Pretty much every submarine move ever made (ok, Das Boot, im Deutsch, gets a pass, if with an asterisk).
There are huge numbers of things that will bother a Reasonably Knowledgeable Individual.
Now, to keep this on topi--Number one bug-a-boo is being able to charge any of the Browning MGs with only one stroke.