There are several gun makers offering rifles chambered for straight walled cartridges. Many of these cartridges were traditionally offered in lever action rifles. In states allowing repeaters, lever actions from Henry or Marlin are popular. More recently we've seen a trend of chambering a straight wall cartridge, usually the .450 Bushmaster, in a bolt action rifle. Ruger, Mossberg, Savage and others currently offer bolt guns in .450 Bushmaster. And, of course, AR-15 rifles are seeing use with the .450 Bushmaster cartridge.