Is "leisurely" still acceptable as an adverb?

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."

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.

Regardless of what dictionaries says about others' usage, I cannot, in general, use any adjectives ending in ly as adverbs (whether with an extra ly or unadorned):

*You're explaining things love(li)ly / good(li)ly / friend(li)ly / ...
(cf, a lovely/goodly/friendly explanation)

Only the most high frequency adjectives in ly are vaguely acceptable as adverbs, yet they require a second ly:

You're running sillily / *silly 
You're singing ?uglily / *ugly

Maybe different regions/ages can behave as the dictionaries describe.

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Sequences of identical affixes are frequently banned crosslinguistically. An example in English is the genitive plural of prince, in which only a single [əz] is pronounced (princ[əz], not princ[əzəz]). When one affix fails to surface, the phenomenon is known as haplology. For leisurely-ly etc., haplology is not available in my dialect, and the result is ineffability. Maybe those dialects that allow adverbial leisurely permit haplology here.

When these noun+ly adjectives like timely, leisurely, homely, slovenly, motherly, and others get used as adverbs, it's hard to hear that as anything but symptomatic of erosion of language skills.

It's just a linguistic reflex, albeit an instilled one, to hear any adjective+ly in an adverbial sense and any noun+ly in an adjectival sense.

She motherly put the children to bed? Not hardly. ;)

When an IRS publication says that filing timely can reduce the risk of penalties, we make unflattering assumptions about the person who wrote that. More generally, such usage generally manages to suggest underdeveloped discernment.

Yet some dictionaries bless "leisurely" and possibly others of its ilk for adverbial use. Who knows, maybe such usage can be traced far back in English history. It nonetheless grates on reflex and on insight into how these words relate to -lich -lig -lik cousins in Germanic and Scandinavian languages. It's really hard not to spontaneously feel that if "couples strolled leisurely in the park" is not symptomatic of modern erosion of meaning, then it must be evidence of historical erosion of meaning.

So while, out of respect for authority, I won't write traffic citations for misuse of "leisurely," I'll nonetheless stick to a structurally consistent usage myself.

Now if we could just figure out where to put "comely"...

I like neither "leisurely" as an adverb, nor "leisurelily", if that were to exist. I replace this and other words that make me feel uncomfortable as adverbs in the same way with the adverbial phrase "in a leisurely manner" etc.

Leisurely is still acceptable as an adverb.

This is opinion shared with top English scholars. One of the most reputable dictionaries, Chambers, lists leisurely as:

leisurely adj not hurried; relaxed. adverb without hurrying; taking plenty of time

Of course, English can be used however you see fit, being a language, it constantly evolves to reflect what is said.

I suggest replacing the grating usage of “leisurely” as an adverb with the mellifluous and unimpeachably correct “unhurriedly.”