Obrez pistol or revolver?

While I'm not entirely certain I think the Obrez counts for bolt action kills, since it's neither a semi-auto nor revolver.

Obrez, from my knowledge, is a modified (cuttoff) Mosin Nagant rifle. More of a sawed-off shotgun, to be more precise. Not sure how is classified in the game, but in reality that was a sawed-off rifle (not necessary Mosin-Nagant).

P.S.: found an article that explains it better.

Well, Obrez Pistol's ammunition in-game is classified as 762x54mmR_Pistol , in comparison to Mosin-Nagant M91's ammunition being 762x54mmR_Bolt. Obrez does fire in bolt-action, though. So go figure. All Medic's guns are considered "semi-auto" for the sake of the medals and assignments, for example, so one would simply have to test this out to make sure of it.

Don't have any medal on me taking revolver nor bolt-action kills right now so can't check for sure.

EDIT: A small test with the "Order of the Golden Heart" I happened to have on Weekly medals currently. The kills were counted for the "Get kills with sidearms" , and on the end result Stats tab, the Obrez kills are counted as "Handgun kills". But curiously, getting 5 kills with the Obrez Pistol granted me absolutely no Ribbon at all. No Lightning Cross (Semi-auto handguns), no St. Sebastian's Ribbon (Revolvers) nor Scout Ribbon of Valor (Single-Action Rifles) . So with this test's conclusion I would say that the Obrez Pistol would be counted as a single-action handgun, hence not fitting into any of the actual criteria for the Ribbons.

If someone does happen to have the St. Sebastian's Order, Lightning Cross Order or Scout Order of Valor available, feel free to test it but considering it gave no progress to Ribbons, I'd imagine it wouldn't give any progress to Medals of the same branch, either.