This is from memory and may not be 100% accurate, but I think the Speer half-jacketed bullets had an entirely different configuration; they were of swc design. Hornady made half-jacketed bullets, but they also had a different nose configuration that what is depicted in the original post. However, many different nose styles were available from C-H and they most likely included the one shown.Didn't Speer make slugs like that, decades ago?
Oops...Half jacket semi-wadcutters, shoot 'em but drive them fast enough so that you don't get a core/jacket separation and leave the jacket in the bore. Use data for jacketed bullets.
If you think Bullseye is clean, try some Scott Solo 1000 (or whoever is making it these days.) If Bullseye is clean, Solo 1K is spic and span.I'm thinking Speer was 200 gr. I remember them. I have some cast 185's that have a longer nose. I almost bet they are designed for revolver use, which would include the Long Colt. In an auto, those may, or may not feed. When I was young I always tried to hot rod the 45 acp. but as I got older, a little touch of Bullseye is pleasant to shoot, relatively clean (compared to Unique anyway), and a lb of it goes a long way.
If they were mine, I would probably try a magazine and if they fed, I would go further, if not, I would pass them on to someone that could use them.