IMO when it's all totaled the cost for your one off 30 caliber will probably cost around 75,000.00 US Dollars. Because you are probably looking at 40 to 80 hours of design work at roughly 150-200 dollars per hour. Then you'll have the costs for writing the various CNC programs and time on the CNC machining centers. Then there are the costs for building duplicates for the Proof testing, having those tests done, and then corrections to the design if the Proof tests reveal a critical weakness. End result may be a 7 shot 30 caliber because of all the "extra" steel you'll need to withstand those 60,000 psi proof loads.
The bottom line here is simple, get yourself a 7 shot, 2 1/2 inch L frame revolver in 357 Magnum. You will save a big pile of money and be able to walk into almost any gun shop and purchase ammunition for your new gun.