I think you have that wrong. The CofG moves forwards, not back when you de-tip them. Unless somehow you have a tip that is as least as dense as the otherwise monometal projectile, and, I suppose, is worth putting on. for whatever reason. Polymer (less dense) obviously has lesser disruption to the balance, between tipped and not tipped.
Well, not to my surprise, an olde fashioned cup and core soft point with the "tip" formed from the lead core, sticking out the front, can do very well. Providing the soft point doesn't get mashed up a bit somewhere along the line.
Aluminium, might be a little easier to make than polymer, for lathe turning people, but its the same thing. Putting on such tips can only worsen the stability factor. Might be beneficial I suppose for boosting the BC, or for some other reason, maybe designed as part of a controlled expansion mechanism, but downsides also.
Visualise the bullets as sort of reverse shuttlecocks. They rely on spin stabilisation, not say drag stabilisation such as an airgun diabalo pellet. They just naturally want to fly backwards. Indeed some experimenters (ahem, military peeps with human sized targets to destroy) used to do just that, shooting old FMJs ,pulled from their military ball ammo then pushed back in again the other way around. They definitely expanded mightily, though obviously the BCs were utter rubbish.
