Originally Posted by Andrew Wiggin
I've got 165 and 180 gr Gold Dots but I have no idea how to tell if the alloys used are the same.
You don't need rocket science to find out all of the above. The lead core will be essentially irrelevant, as they are swaged, and almost always at or near pure lead. The jacket provides the structural hardness, and bonding, if applicable, is either by soldering (heating), adhesive, or both. The difference between "hard" or "soft" pure lead is so far below what is considered "hard" (such as hard cast), it just doesn't matter to a degree we (consumers) can measure. Hardened lead (alloyed) is not ideal for swaging, and would lead to inconsistent finished bullets, even in a laboratory type process. Most bullet mfg's (such as Hornady) claim to use pure lead for the core. Of course, there are exceptions, but these would be classified in an "exotic" category, and apply mostly to non-lead, non-toxic bullets (some Winchester non-lead have a pure tin core).
To determine the core (lead) weight, peel the jacket from the core and weigh it. Or, you can melt the lead out of the jacket and weigh the pour.
To examine the jacket, hold a bullet with long pliers, and use a propane torch to melt out the lead. Keep the temperature at just enough to melt the lead, without damaging (burning/melting) the jacket. Once the jacket is empty, it can be weighed, and mic'd for thickness. Measure the base, as it'll be the most likely common section of differing bullet weights (they may use the same cup/blank for different bullet weights). If you want to test the jacket for hardness, do it before heating, or molesting in any other way.