When someone is making a smooth sided mould to try something out or for paper patched boolits I can never figure out why they don't just follow the old Ideal Cylindrical mould style:
You do not need a split mould to make a smooth boolit.
They are simple to make and work well. I have made several from .30 cal to 12 ga.
I make mine out of 1 1/2" round bar though so they hold heat better and to allow for large slugs like 12 ga. Most of mine are also a bit simpler in that the nose form is simply "shimmed" with a spacer to provide the weight I want and basically is an ejector to ensure I boolit can be pushed out of the mould. Some I have made as HP moulds with the HP pin being the ejector.
For paper patching they can remain smooth. For shooting lubed they can be made a little over groove diameter then can be tumble lubed successfully and if made a few thou undersize they can be knurled, which increases diameter by about 0.003", then tumble lubed which works even better.
I make a "D" bit in the shape and final diameter I want then drill and or bore to close size, then run the "D" bit in by hand to finish... then usually lap to final finish.
They are easy to make and they work.
Longbow