aqua regia from homebrewed 50% nitric acid?

[dbrick81]

IF I remember right aqua regia is a mixture of 3 parts HCl and 1 part 70% nitric acid. If I was going to make AR from Steves cold brewed 50% nitric acid, how much HCL would I add to it and how affective would this AR be compared to the stuff made with 70% nitric? Also, Will I'm thinking about it, If I was going to dilute a liquid from say 100% to 75% with water, would the water be added by weight or volume?

Thanks,

Davey