Strike Doubling

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Strike Doubling, also known as machine doubling, is a doubling effect created on a coin's device(s) during the strike itself. Paraphrasing Van Allen, strike doubling creates "flat, shelf-like shiny tops that narrow the device." This is in contrast to die doubling, which shows "rounded tops that widen the device."
Strike doubling does not create a new VAM since the effect is likely on the one coin only and is not the result of a different die variety, but likely from loose dies.
Also know as Strike doubling, machine doubling, machine damage doubling, SD, MD, MDD, ejection doubling, shelf doubling.
The links below are to the National Collectors Association of Die Doubling educational articles showing differences in types of doubling on coins.
http://www.reocities.com/ncadd/educational1.html
JT Stanton Flyer http://hermes.csd.net/~coneca/content/StrikeDoublingFlyer-PDF.pdf
Please click this link for the full VAMworld.com definitions page.
thread with date digits and ejection doubling http://www.vamworld.com/share/view/78672545
Below are examples of machine doubling. Notice all have the same flat, shelf-like look.
00o v41a strike doubled mintmark md 22 dec 2010.jpg Kam-1888o-dblrev-092712.jpg
1922-P sd 22 22 dec 2010 md.jpg
1922-P sd Iray 22 dec 2010 md.jpg
1922withdoubled2s037 md 22 dec 2010.jpg
ARS 1881 O SD 1 md.jpg
ARS 1881 O SD 2.jpg
ARS 1881 O SD 3.jpg
Kam-1888o-dblrev-a-092712.jpg
Kam-1888o-dblrev-b-092712.jpg
ARS 1884 S SD 3 md.jpg
ARS 1922 P VAM1 1 md.jpg
ARS 1922 P VAM1 2 md.jpg
ARS 1922 P VAM1 3 md.jpg
ARS 1922 P VAM1 4 md.jpg
Grw1900 O 14A RPM-1 22 dec 2010 md.jpg
Ken 1793 machine doubling 22 dec 2010 6 - Copy.jpg
Ken 1793 machine doubling 22 dec 2010 6.jpg
P1020803 22 dec 2010 md.jpg
P1020807 22 dec 2010 md.jpg
P1020811 22 dec 2010 md.jpg
Please click this link for the full VAMworld.com definitions page.