I bought a sidefolder kit from Ohio Rapid Fire. I am not sure if the stock section is Bulgarian or Russian. The rear of the stock is ribbed and has an arsenal mark that looks like a circle with a U inside it. There is another mark on the inside of the trunnion in the shape of a square with a U inside it. I really need to know this before I buy a flat for this kit. I was also told that you can tell by the pin diameter size. Any help would be appreciated. Thanks.