HMMMMMM... I don't recall that.. but then I really wasn't too interested in Iver Johnsons. Looking at the cylinder I see normal locking slots for the cylinder lock snap and I fail to see why they would drop a proven technology in favor of a possible haphazard locking method at the time most dangerous... when the gun is discharging.
It may be that the model 1900's early model had a weak lock snap and it is often broken on those early models.
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Iver Johnson Arms & Cycle Works - Manufacturer of sporting arms since it started as Johnson, Bye & Company in 1871 at Worcester, Massachusetts. In 1883 became Iver Johnson & Company, and was again changed to its current form in 1884. In 1891 the firm moved to Finchburg, Massachusetts.
Some Tradenames used by Iver Johnson Arms & Cycle Works:
AUTOMATIC HAMMERLESS Tradename used on double action hammerless revolvers by Iver Johnson.
BOSTON BULLDOG Tradename used by J. P. Lovell & Sons on revolvers made by Iver Johnson.
CHAMPION Model name used by Iver Johnson on shotguns.
DEFENDER Tradename on revolvers made for J. P. Loveli Arms by Iver Johnson, c.1880.
EAGLE Tradename used on revolvers by Iver Johnson, c.1879-86.
EXCEL Tradename used by Iver Johnson.
EY Code following the model name on arms made for Montgomery Ward by Iver Johnson.
GEM Tradename used on pistols, c. 1870 marketed by Stevens Arms & Tool Company, and possibly made by them. This name is also attributed to Iver Johnson and Bacon Manufacturing Company.
HERCULES Tradename used by Montgomery Ward & Company on arms made by Iver Johnson.
KNOX-ALL Tradename on shotguns made by Crescent Fire Arms Company, and later on shotguns by Iver Johnson.
Lovell Arms Company c. 184091 in Boston, Massachusetts. Became J. P. Lovell & Sons about 1870, and was possibly absorbed by Iver Johnson in 1868 but allowed to operate under its existing name.
SECRET SERVICE SPECIAL Tradename used by the Fred Bifflar Company of Chicago, Illinois on revolvers made by Iver Johnson and by Meriden Firearms Company.
SIMPSON Tradename on revolvers made by Iver Johnson for J. P. Lovell & Company of Boston, Massachusetts.
SMOKEY CITY Tradename on revolvers made by Iver Johnson for J. P. Lovell of Boston, Massachusetts.
SWIFT Tradename used on revolvers by Iver Johnson, c.1900.
UNCLE SAM Tradename used by Iver Johnson, and also by J. Palmer O'Neal Company of Pittsburgh, Pennsylvania.
U.S. REVOLVER CO. Tradename used by Iver Johnson on revolvers.