Johan and others:
Having researched the 38th NYSV and actually owning a microfilm copy of the National Archives rolls in my collection the uniform of the regiment is as follows:
M1858 Forage Cap
M1858 N.Y. State Shell Jacket - A 9 button variant. In a N.Y. Times article of June 1861 it mentions that the 38th wore a jacket similar to the 9th NYSM which was 9 buttons. A picture of Sgt. Martin Baxter located in the Putnam Valley Historical Society shows one of these coats. As with other New York jackets it has piping around the neck, epaulets and belt loop, but also as a light blue piping "chevrons" near the cuff, as is seen in 1863 National Guard Jackets.
Trousers were initally dark blue. By late summer 1861 these pants were replaced with the light blue variety.
Gaiters- from the regimental muster rolls the gaiters were black leather affairs. Similar New York regiments in the 3rd Corps were also issued these such as the 37th and 40th NYSV.
Accoutrements- Standard cartridge box for rifles probably the Model 1858. The regiment initally carried 1855 Rifle muskets. These boxes were carred on leather straps over the shoulder instead of on the waistbelt.
Knapsack- An 1855 double bag, canteen 1858 smoothside and gray blanets.
As with other regiments the 38th was issued white havelocks from well meaning New Yorkers, but if they wore them is uncertain.
Their colors were an interesting set. They carried a City of New York blue regimental, which displayed the arms of the City of New York, and a wool bunting national with a likeness of General Winfield Scott painted in the blue field, probably as a token of their nom-de-guerre "The Second Scott Life Guards."
Hope this helps,
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