Raimey,
I don't have a practical way to determine if there is a velocity difference between Boxer and Berdan primers. I can't change primer type without also changing case type/make, which has the potential to vary the velocity due differences in case volume. The differences in velocity can be measured, but I don't know which variable to attribute the difference to, or if they balance each other.
This has been a pretty long thread; can you refresh my memory? Did you slug the barrel yourself? Did someone else? Was the groove diameter assumed to be the current normal 6.5mm (.264") standard? The expected groove diameter of a 6.5x70R barrel is .260-.261" and the use of an oversize lead bullet may not create a problem, or only something minor such as leading. Jacketed bullets, however, are not as forgiving and if they are too large to allow the case room to expand and release the bullet, excess pressure can result. Another consideration is bullet length, with modern bullets. The original bullet was round nose and a modern spitzer bullet of the same weight would likely be too long for the rifling twist. Even with these considerations, I don't expect you will have a problem finding a good load.
Good luck, let us know about the Springer when it arrives.
Mike
