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Lead would be a lower starting and maximum load
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This is generally incorrect. Lead has less friction than copper so takes more powder than it's jacketed counterpart to get it up to speed. More friction from the copper means it sits still in the case longer, raising pressures more before it starts moving. Copper takes less powder than lead for equivalent speeds.
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Not quite. you are both somewhat right, and wrong...
In a semi auto Edward429451 is partly correct, assuming the same powder, the starting and max loads are generally pretty close, so long as the copper speeds are not too fast since i think the general consensus is to keep lead below 1000fps to avoid leading. The last statement though "
Copper takes less powder than lead for equivalent speeds." is incorrect, from what I can see, they are always pretty close, in a semi auto, Sometimes copper will take a minute amount more, sometimes lead.
but in a revolver, m&p45acp10+1 is correct that the starting and max loads for lead are almost always significantly lower, but both still achieve the same speeds.
Why? Its all about the gap. In a semi auto, the copper bullet has the benefit of the combustion gasses pushing on it all the way to the muzzle, It gets the same speed as the lead, because even though (or perhaps because) lead is easier to push, the increased friction from the copper means higher pressures. But in a revolver you get that first initial push and that's it, then the increased friction from copper comes into play, slowing it down all the way out of the barrel, which means that first initial push has to be bigger to get the same speed.