Hey 4,
When I first got a 7.62X54 Russian, I also had some problems finding Boxer primed ammo. I had a bunch of .303 Brit, however, and I thought I might try to make some Russian ammo out of the Brit ammo. The .303 was a bit smaller than the Russian as RC mentioned earlier, but I thought I would see if I could fireform it to the Russian chamber.
I sized the .303 in the Russian die, and I guess I probably had to trim it to length. I then charged the .303 case with a very light charge of probably 2400 powder, added a 155 grain cast bullet, and touched it off.
Listen to what RC said. My .303 want to be 7.62X54 Russian expanded the case so far it split from the shoulder to near the base. It was a very light charge, so the rifle held together just fine, and in spite of the case splitting that much, there was no gas coming back from the chamber. The bullet flew down range, but it was clear the .303 was not quite big enough to make into a Russian.
Not long afterwards, Southern Ohio Gun had a sale on new Boxer primed 7,62X54 ammo, and I bought a case from them. I think it is always better to buy reloadable ammo rather than fireforming cases if reloadable ammo is available somewhere. Wait a while, and you will find it.
Best wishes,
Dave Wile