We just started testing a new .50 BMG caliber gilding brass gas check. We borrowed a NOE 850gr .514 mold from rockrat on the cast boolits forum. We just sized one for the first time with a .104 tall .517 gas check. The bullet came out at 838 grains with a 50/50 wheel weight / linotype alloy mix sized to .512.

Here is a picture:

Our idea for this .50R gas check was to make it in a mid size so you won't need separate Short and Tall versions. Testing has just started, but the fit is very good. After using a gas check seater we can't pull them off by hand. So far, they have sized fine at .512 and .517 using a push through NOE bushing type sizing die.