Tom,
Did you read the article in WAIDMANNSHEIL issue #46,Summer 2011, entitled 11mm Ammo and Rifles? If 8x50R Lebel is too short, and it is shorter than 45-70,you may have to go to 348 Win. or 50-95/50-100. These would require sizing the head a good bit to get smaller than.536"( 348 may be a seasonal item, but Starline should have 50 cal. for BPCR shooters). Do you have an arbor press in your shop? You really need a chamber cast. It wouldn't be fun if you could buy ammo in Walmart.
Mike