Is "leisurely" still acceptable as an adverb?

Solution 1:

My dictionary shows the word as both an adjective and an adverb:

leisurely
(adjective) acting or done at leisure; unhurried or relaxed : a leisurely breakfast at our hotel.
(adverb) without hurry : couples strolled leisurely along.

In your example, it makes sense to use the adverbial form. Why? An adjective would have to modify a noun. What noun would it modify? The writer is not talking about a leisurely projectile, a leisurely wound, leisurely skin, or a leisurely skull. The only thing leisurely in that sentence is the ripping action.

As for describing the formation of an exit wound as leisurely, I don't know if that sounds archaic. Instead, I see the pronounced irony as intentional, as a way to comment on the mood of the director's film.

Solution 2:

According to Wiktionary, leisurely is acceptable as an adverb.

[...]

Adverb
leisurely (comparative more leisurely, superlative most leisurely)
In a leisurely manner.

Oxford Dictionary of English has an entry of "leisurely" as adverb: "without hurry."