yeah the 338 rum is 100 thou shorter than the 7mm or 300 rum, just like the 300 winny is 100 thou longer than the 264 and the 338 winny's. as allan said the 338 edge is just a simple neck up, not sure what the difference is in the +P version, the 338/300 Rum IMP. is known as the 338 O'Brian.
RR