There is an article in the latest Handloader Magazine (#281, December 2012)about the perils of bullet sustitution. It describes pressure testing experiments by Dr. Lloyd Brownell in the 1960s, where he was trying to produce equations to predict pressure, etc. from cartridge/gun/load parameters. He came across one situation where two bullets of the same caliber, weight, shape and construction TYPE produced VERY different pressures.
The troubling bullet was a 105 grain Speer roundnose bullet that looked to be about the same shape as bullets from Hornady and other manufacturers. However, it developed much higher pressures. Substituting that Speer bullet in data for the other bullets could result in pressures of 125,000 to 163,000 psi. This result was predicted by the equations that he developed and then verified by actual pressure testing, so it is not just a theory.
Speer explained the behavior of their bullet as being due to thicker jacket walls, stiffer heels, and long caliber diameter section than bullets of comparable weight.
How many of us can look at bullets and tell how they will behave under pressure?