Originally Posted by
1hole
Larry, I don't know what you tested nor how. I have no such "test" data, and you know it. But I am an old space electronics system tech and I do have a detailed analytical approach to technical questions.
The OP stated his concern about dangerous pressure spikes from a minor seating depth change; I only addressed what he said, not all possible events. (And I don't think it's necessary to blow the barrel off to qualify as a "blow-up".)
The OP was specifically concerned that a (very small) change in his .45 ACP seating depth might be dangerous; it is not. Your mention of a .200" seating change is not small.
First, modern 9mm and 10mm cartridges pressures normally run very high and their case volume is quite limited. So, by (Boyle's Law) of physics, we know that small decreases in volume can make oversized differences in pressure. But that volume effect simply isn't a player with our older pistol cartridges so, IMHO, the OP need have no fear with normally loaded .45 ACP.
Second, the only real "spike" in chamber pressure occurs shortly after ignition and that comes before the bullet has moved much. Anything such as crimping that retards initial bullet movement will increase the peak start pressure. Your mention of seeing massive bullet set back because of cartridges hitting the feed ramp says those bullets were held so loosely they could not have appreciably resisted forward movement so the shortened seating depth, as such, couldn't have amounted to much.
Finally, I cannot imagine having a normally loaded bullet seated so loosely that simply chambering the round would cause .200" of set back. BUT, if it happened, that same loosely held bullet would also move forward very easily to expand the volume of the combustion chamber and that rapid volume increase would have greatly reduced the attainable pressure.
So, no; small changes in the seating depth of older modest pressure cartridges are not dangerous.