Yep, I agree with getting a 6mm wildcat that is based on the 30-30 parent case. Brass for the 225 is twice as much as 30-30 brass, plus I have never picked up any 225 brass at the shooting range! I have recovered hundreds and hundreds of once-fired 30-30 brass.
Many years ago there was an article in Handloader Magazine about the 6mm Bullberry. I looked for that copy, but I couldnt find it. I have them all so I know I have it but just cant locate it. At that time or thereabouts, I was looking for a unique cartridge to shoot in my Contender. This 6mm Bullberry looked very inviting. But I settled on another cartridge based on the great little 30-30 case. It was developed by some guy named Watersthe rest is history and I have never looked back! Good-luck
BCB