Original US Military Machine Guns on the Civilian Market (w/ John Keene)

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Today Ian is back with NFA specialist John Keene of the Morphy Auction Company to talk about US military machine guns. Specifically, how intact and original examples end up in the civilian market. Some models, like the Reising, as very easy to find in completely original condition (almost hard not to, really). Others, like the belt-fed Browning 1917 and 1919 models are very rare in original condition, and are almost always found as parts kits built on newly-registered receivers. What drives these differences?