Cast, depends on what freebore your reamer has. Mine is .180” saami length freebore and I can fit 180 & 195 in the factory ultra mag box a 3.65”. If you have longer freebore you can install a longer Wyatt’s box to give you more room.
And yes you can use a regular magnum action but the feel rails have to be slightly opened up. I open them up with a file by hand and keep checking until the case fits through the feed rails.