Breechplug

In the wonderful world of ML barrels - there are no standards. One companies 50 cal may not and probably will not have the same bore diameter as that of another company. Even within the company the 50 cal bore may vary from .499 to .502/3. Since there is not an exact standard it does allow the manufacturer to extend the use of some cutting tools and does not require a tight inspection system.... benefit - less expensive.

That is the reason for all the different sized sabots.