This Sturmtiger from Panzersturmmoerserbatterie 1001, was captured on Feb. 28th, 1945, near Reichswald, Germany. It's chassis number is 250327, which means it was built as a standard Tiger in June of 1943. It has 31 gas openings, as opposed to 20 of the prototype, 39 in early production vehicles and 30 in late ones. It also has 9 groove rifling, the later type barrel sheath with the chevron-shaped undercut and fitted with both sets of muzzle projections. There is a surprising amount of variation in the 18 Sturmtigers that were built. The Kubinka Sturmtiger is somewhat unique and has features not normally found on the others. One prototype, 12 series-produced between August 13th to September 21st, and a final 5 in December 1944. This is one of the 12 series-production models. It uses earlier model, large diameter idlers, (late models used the smaller idlers) and has a soft-edge "Ambush" scheme paint job with only a few rather large Dunkelgelb spots.
A good reference for this is TankPower Vol 16, though the book has a few mistakes.