I have heard and read the term SMALL BASE RESIZING in reference to brass fired from machine guns needs to be SMALL BASE RESIZED. Also I understand that it is recommended for most semi-autos. I cannot find the defition for this. How is this done? Thanks for the help.

A small base die is only made a little smaller diameter at the base, where trhe case web is. You use it just like any other die, but it squeezes the base a tad smaller than a normal die, to insure it functions thru semi-autos. They are only made in several popular cartridges, not all of them.

Small base dies are not needed about 99% of the time. In 223rem, i have fired many different makes of semi and 1 full auto rife with out any problems, using ammo loaded with RCBS standard full length sizing die set. There was one time when small base dies were needed. This gun was a Rem 7600 in 30-06. The chamber of the rifle was defective, its was oval/out of round . A small base die is nothing more then a full lenght sizing die with smaller demensions.