Originally Posted by Aloxite
Now I'm certainly no expert. So take my post with a grain of salt.
My understanding is that the idea is to start with some rounds that you know are within pressure specs. Fire those rounds in your pistol. Then measure those rounds and use that figure for your load development.
So take some hot factory rounds like Buffalo Bore or Double Tap and fire those in your weapon. Measure that. If your reloads show the same or lower case head expansion then you are within the same pressure range.
Otherwise it seems like the individual chamber of the barrel is going to influence how much expansion you see.
I agree. To tighten this up even further, look up the Ken Waters method if you have not done so already. MMA10 has a great summary that is found here:
Benchmarking with hot factory stuff is especially useful if the intent is to load in brass of the same type and manufacturer. Different metallurgical properties of different brass makes - even regular Starline vs. nickel Starline like DT uses - will yield different expansion characteristics.
Many of us use Starline brass so Buffalo Bore is a good data point for these purposes.
In a loose Glock chamber, it is easy to see a trend of max case expansion from min to max. Mine trend very consistently with Starline brass. IMO, this is the single most important part of analyzine loads during workups.