Today I did some measuring between a 7.62 AMD, 7.62 Romy, and a 5.45 Bulg. bolt lugs. The AMD and Romy were within .001 of each other so we will just call them the same. The 5.45 has the smaller stem then the 7.62. What I'll call the small lug is the one away from the extractor. The width and height are the same between them on either caliber. The difference is in the length. The AMD/Romy is .402 long and the 5.45 is .551 long. The large lug where the extractor is located is .611 long on the AMD/Romy and .720 long on the 5.45. The bolt face hole on the AMD/Romy is .458 and the 5.45 is .400. Both would need to be opened to around .475 for the 308.
Rbthntr64, does that sound like the measurements on the Vepr? Also didn't the Saiga 308 use a small stem bolt?