They used a 300gr shot from a pistol with two Pyrodex pellets. A 50gr and a 30gr equivalent for 80gr total.

WHC is sponsored by CVA/Powerbelt and so is the other forum they mentioned.

Notice how the gel block showed very little temporary distortion in the slow motion video.

Did you see them mention the fps at impact?

You can have all this for $25/15 plus the cost of the Optima V2 pistol or a greatly reduced load from a rifle.