M99 or M-99 may refer to:
Places
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M-99 (Michigan highway), a state highway in south central Michigan
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Messier 99, an unbarred spiral galaxy approximately 60 million light-years away in the constellation Coma Berenices
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M99 road (Johannesburg), Metropolitan route in the City of Johannesburg, South Africa
Rifles
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Barrett M99
The Barrett M99 (Model 99) is a single-shot anti-materiel rifle that was first introduced in 1999 by the Barrett Firearms Company as a less expensive alternative to the company's higher-priced offerings. The rifle uses a bullpup configuration wi ...
, a sniper rifle
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Zijiang M99, a Chinese anti-materiel rifle
Tranquilizer
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Etorphine
Etorphine (M99) is a semi-synthetic opioid possessing an analgesic potency approximately 1,000–3,000 times that of morphine. It was first prepared in 1960 from oripavine, which does not generally occur in opium poppy extract but rather the r ...
(a.k.a. Immobilon or M99), a veterinary tranquilizer
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