For most of my CAS and repro unlined holsters I use 8-9 oz. Tandy/Leather Factory topgrain veg-tanned cowhide. For lined holsters I generally use 6-7 oz with a 2-3 oz or even 3-4 oz veg-tanned, smooth side to the gun. Use Barge cement and weight down for several hours. For heavy guns used for hunting, my #96X series holsters when unlined, I will use 10-11 oz.
Stay well and safe, Pards!