I opened up a .378" bolt head and it works fine for the 7.62x39 I just built. As a matter of fact I didn't even have to mess with the factory extractor.

I used a Stevens 200 chambered in 223 for the build. It feeds from the magazine great and ejects fine.

You could also use a .473" (308 Win) bolt head with SSS's PPC extractor. Most times the factory extractor will work but you might get a failure to extract from time to time. That is why SSS's extractor is wanted.

Dolomite