Please Note: There are three different gas checks for 40-41 cal. molds and one especially for 40 caliber molds.
#1 .41 Lyman type, the shank will measure .397 and is used on all .41 caliber Lyman molds and a few custom molds.
#2 .416 Rifle – the shank will measure .393 and these gas checks fit .41 caliber RCBS, Saeco and some custom molds.
#3 .41 BSS – the shank will measure .379. This is a new gas check that has been designed especially for .41 bullets. Many of the custom mold makers are now making molds for the improved .41 BSS.
#4 .40 BSS is a gas check especially made for .368 shank 40 caliber bullets.
NOTE: The shank diameters may vary by one or two thousandths from the diameters listed above.