Most bullet alloy shrinks slightly as it cools, so if the inside was well polished, it probably didn't stick bullets, even without taper.
Keith;
In regard to this statement, Ross Seyfried once in an article in Handloader magazine described what he referred to as his "Magic Bullet Mould". It made a grooveless bullet for paper patching & simply involved cutting the cavity in a solid aluminum block. He simply used round bar stock & the reamer had the nose form on it with a cylindrical body.
After the lead had set enough to cut the sprue the mold was inverted, given a slight tap & he said the bullet would just slide out. I have not tried it but will take his word for it, which goes right along with your statement.
