.25-35 and 6.5x52R are supposed to be the same case. I bought some Sellier and Bellot 6.5x52R but they will not chamber. I compared to 25-35 of Winchester manufacture and there is a difference in the angle of the shoulder and the position of the neck. I pulled the 6.5x52R brass and ran it thru the lee sizer die but the shoulder would not set back enough to chamber in this rifle. Is my die bad? Winchester brass loads and fires fine (facory new or reloads). I expected the die to reset the shoulder to the same spec as the winchester brass. Any ideas?

BTW, I bought the S&B since it is half the price of winchester stuff and my twist rate is so slow I can not shoot the 117 grainers anyway. They keyhole. 86 grainers shoot VERY well.

I would like to use the S&B brass to reload,

A .25-35 Winchester is almost identical to the 6.5x52R. The 25-35 Tomcat, on the other hand, has a blown out case with sharper shoulder. The rim of the .25-35 Winchester is 0.506" diameter, same as the .30-30, from which the Tomcat cases are usually formed, but the 6.5x52R has a rim diameter of 0.496", leaving you have a 0.010" difference that won't be a problem to put in the Winchester chamber. The 6.5x52R uses a 0.259" diameter bullet (nearly a true 6.5 mm, while modern 6.5 mm bullets, such as the 6.5x55 are, at 0.264", nearer to 6.7 mm). The 25-35 Winchester has a 0.258" bullet. Too close to matter. The .25-35 Tomcat uses a 0.257" bullet.

I think maybe you have the Tomcat version of the .25-35, and not the .25-35 Winchester?

What type of rifle are you shooting this cartridge?
THe 6.5x52R is supposed to be .25-35, with a metric designation.
Another question that comes to mind is your Lee sizing die. Is this a full length sizer, or the one from the Lee Loader set. The Lee loader only neck sizes and cannot push the shoulder back to factory specification.