is a "Ma Deuce" (M2) ".50 BMG" -- (full auto) Browning Heavy Machine Gun.
That is no "..50-caliber sniper rifle"!
That beast certainly didn't come through any "civilian gun shop" that I have ever encountered. Almost 100% certainly , it was stolen from some military unit -- or "donated" by ATF...
That M2 appears to be "NIB" ("New -- In Box"). The one on my son's "track" dated back at least to WWII...
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Please don't tell me the BATFE is supplying brand new full auto .50 BMGs to drug cartels!