Can the "Gatling" be countered by "Missed!"?
Using the FAQ here the following question and answer says,

Q19. How many Missed! cards are required to cancel a Gatling played by Slab the Killer?
A. Only one. The special ability of Slab the Killer applies to BANG! cards only.

For reference Slab's ability is &quot;Players trying to cancel his BANG! cards need to play 2 Missed!&quot;
This would infer to me that a Missed card can be used against a gattling as the question says that one card is needed to stop it.
There is also This thread on BGG which goes into detail saying a Miss can be played.  It makes the distinction between a bang card and a bang action so whilst you can only play one Bang card you can play multiple cards with bang actions and any bang action can be missed.