Do you have a WW1 Model 1897 trench gun or a WWII Model 97 trench gun? The stocks are slightly different on each.

On a WW1 trench, the swivel is 3" from the end of the stock (excluding the buttplate). On a WW2 trench it is 3 and 3/8". Keep in mind that the swivel is neatly inletted into the stock.

Hope this helps.

TD