There ARE a few differences in the 303B and 35Win cases. The Brit is 2.21" long and the win is 2.41". Brit base is .458 ,win is .467". The rims are Brit=.530 and win =.539" The biggest worry would be the .009" difference in the bases. IF (big IF) you keep the pressures down to below the 45,000 # level it SHOULD work even though it is short by about .020. How sound is the gun you plan to use this in? That will also affect the ability of the gun to handle the reloads. Just remember ,YOU ARE RESPONSIBLE FOR YOUR SAFETY. And that of bystanders when you shoot the gun!
