A Pen gun is a firearm that resembles an ink pen. They generally are of small caliber (e.g., .22 LR, .25 ACP, .32 ACP, .38-caliber, etc.) and are single shot. Early examples of pen guns were pinfired, but modern designs are rim or centerfire. Some pen guns are not designed to fire regular cartridges, but rather blank cartridges, signal flares or tear gas cartridges.
In the United States, pen guns that can fire bullet or shot cartridges and do not require a reconfiguration to fire (e.g., folding to the shape of a pistol) are federally regulated as an Any Other Weapon (Title II). They require registration under the National Firearms Act and a tax in the amount of five dollars is levied.
- John Minnery (1990). Fingertip Firepower: Pen Guns, Knives and Bombs. Paladin Press. pp. 33, 38. ISBN 0-87364-560-X.
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- J. David Truby (1993). Zips, Pipes, And Pens: Arsenal Of Improvised Weapons. Paladin Press. p. 132. ISBN 0873647025.
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- Stephen D. Carpenteri. Gun Trader's Guide, Thirty-Fifth Edition: A Comprehensive, Fully Illustrated Guide to Modern Firearms with Current Market Values. Skyhorse Publishing. ISBN 1626360251.
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- "National Firearms Act Handbook" (PDF). Retrieved 2014-02-18.