What nail gun would have been used here?

I'm looking at replicating this merbau fence.

It looks like they've used a nail gun to hold the decking in place then afterwards run a chalk line and pre-drilled and screwed them in place. Seems easy enough.

I was curious though, is there a way to do it without a nail gun, or if not, what type would have been used for this? Framer/16g DA or C / 15g?

I've been toying with buying a nail gun for a while to do some other projects (putting up some Linia Scyon cladding) so it might finally make sense to get one if I can use it for two or three other jobs!