As you move to smaller handguns, you lose alot of performance. The 380 caliber is optimized for shorter barrels and yields around 950 fps with a 95 grain slug out of a barrel of similar lenght to a sig 230. When you look at 45 ACP in so called sub-compact or micro firearms which feature a barrel lenght of 3-3.5" inches the 45 ACP begins to suffer a lot. You achieve velocities in the neighborhood of 700 fps with a 230 slug. I doubt that such a wide slug moving so slowly has much penetration...
My point is not that 380 is somehow better than 45 ACP, but rather that most calibers will give mediocre performance in such short barrels. Both a 45 or a 380 will working in a small gun, but they will both work fairly poorly. Plan for this and act accordingly... If it fits in your pocket, it's no laser beam of death...