WWB .45 and UMC JHP .45 are equal
Out of curiosity I went to the Winchester and Remington Ammo websites and looked at the ballistics on Winchester White Box FMJ .45 and Remington UMC JHP .45, and they are identical. Both types push a 230 grain bullet at a muzzle velocity of 835 feet per second, for muzzle energy of 356 foot pounds.
So I don't think the problem with the UMC is less zip than the Winchester. I would suspect that the UMC hollowpoint is scraping on the feed ramp and slowing down the slide a bit.