A customer is experimenting with aluminum gas checks for the 585 caliber, made with the FreeChex tool. The dimensions did not come out quite right on the first try, though it should shoot fine anyway thanks to obturation.
If I were designing the checks from scratch, I'd aim to make the installed OD 0.005" - 0.010" over sizing diameter, so they'd crimp on in the sizing die.
I'm the guy Dan made these moulds for. I've finally got my 585 Nyati finished and have been shooting it with these cast bullets. Dan also made me a 750 grain and a 900 grain version at the same time. So far, I've had the 900 grain one up to around 1700 fps without any problems and very good accuracy.
The 650 grain one above has been loaded with Trailboss for about 1420 fps. My 12 year old son can handle those loads pretty well.
We have recovered quite a few projectiles from the range still with the gas checks attached, which was quite a welcome surprise for me.
As usual with Dan's moulds, they cast very easily, fall from the mould well, and shoot better than I can.