since 303 british is getting hard to find I am wondering if there is any demand for cast bullets out there. I have a lyman 314299 mold and if demand is good I will start a run to sell on here.
I used to own most of the toys for casting bullets - and, I was doing a couple purchases to Jet Bullets - sold all the stuff that I owned - was too handy to be able to just order what I wanted - .368" and .459" - I never did enough purchases to keep Jet Bullets in business, but a correspondent from Winnipeg bought much more quantity than I did. The aspects to consider - why we liked that source - was apparently foundry certified lead or alloys used, bullets that I received were sized, lubed and gas checked. From my acquaintance, it sounds like he would receive his orders "as cast", and preferred to size, lube and install checks (if needed) himself. Sounds like you have a "good" mould and "good" idea - I think that Jet Bullets had dozens of moulds, sizers, etc. You might want to cruise through the Accurate Molds website catalogue - custom made moulds from brass or aluminum - I think - I had about 3 of them at one time or another - I think they are fine to use - also stole some "break-in" ideas from Lee brand moulds. So, you will need space to be set-up, and time for casting, sizing, lubing, handling orders, shipping, etc. at a "shipped price" that customers would pay.
My own experience is that once you have the melt to temperature, the moulds to temperature and into a casting rhythm - does not take much to turn out a couple hundred "as cast" bullets - then is several set-ups / ways / tooling to size and lube them and/or install checks, or powder coat. I am sure it would all come with time - as is, I still have a .312" and a .314" sizer for the plethora of ".303" bullets previously cast from wheel weights - and then customers will want weights likely between 150 grains and 215 grains (or higher or lower or anywhere in between) - would be up to you what you chose to make and sell? Might want to read through Richard Lee "Modern Reloading" about his thoughts of "hardness" (alloy?) versus breech pressure.
Set aside / plan for time to deal with customer complaints that your product is crap - often times from someone who does not thoroughly scrub all bullet jacket residue from their bore before firing cast lead bullets - seems to be a thought among some to be able to fire off half dozen cheap surplus FMJ bullets and then use the cast bullets. I read of some shooters who dedicate certain rifles ONLY to cast lead bullets - for that reason.