Here's a quote from the chapter's beginning:
"The Officer's model category of revolvers represents one of the most involved and perplexing categories in the entire Colt field.
Although not made in a wide variety of calibers or barrel lengths, the myriad of other variant details makes one wonder how the company itself was able to keep their records straight."
Your barrel marking is what I used for dating the time frame of production.
The 'Officer's Model' first saw light of day in 1905, with serial number beginning in the 241000 range, with the 'Army Special' starting in about 1908 within the 291000 range. (information from the chapter titled - 'The Models 1892, 1894, 1895, 1896, 1901 and 1903 New Army and Navy Revolvers')
There is no mention of a 'prototype' or 'variant' - they share the same frame configuration, and it's long been well known that Colt used 'everything' in the Parts Department when at all possible, to avoid waste and needless cost.
In 1930, the designation was 'Officer's Model Target'.
Vaya,
Scouts Out!