I keep reading where reloaders state that the mfg's have either changed the way they measure pressure (cup vs psi/strain gages/etc) or changed their powder formula.
The #1 reason for conflicting data, outdated data or removed/reduced data is the changes in how the cases are made. Every time a mfg changes the font on a case (caliber stampings on base of the cases) it signifies that a change was made in mfg of that case that has changed it's reloaded. Some of the changes (but not limited to) are changes to the wall thickness, base/web thickness, web shape (cup) primer pocket thickness, etc. Any of those changes will effect the case volume, hence changing the load data/powder charge. Some of the minor changes are the addition of a cannalure or base angle/shape/roundness for the automated reloading machines, increase or decrease in the # of steps taken to form/make a case, etc.
A good example of this is what I used to load decades ago. Used to shoot skeet every now & then, used a 20ga. Loaded ww aa cases with ww primers & ww aa20 wads with a load of 14.3gr of greendot powder. My brother calls me last year & wanted to know what I used to use for skeet loads, he wanted to use up a bunch of 20ga wads he had laying around. I told him the load above & a couple of weeks later we're talking about something & he brought that load up. He said he couldn't find it in any of the new manuals so (He's always done this for decades) called alliant & asked them about that load. They told him flat out, DON'T USE THAT LOAD!!!!! He asked them why, did they change the powder? The rep replied heaves no, ww changed how the make their cases.
So when you see older data, don't assume they measured the pressures wrong or they are making the pressures different now or the lawyers say to drop it down, etc.
With the "new" firearms with the unsupported chambers & lite alloys that have come out in the last 20 years alone with the new high energy powders. The mfg's have reacted to the safety issues (stronger webs/smaller case capacity) along with using modern powders that are giving the same velocities as their older counterparts but have less pressure.
I'm not saying that some of the older loads/data was flat out stupidly wrong. I just wanted to point out the thing that changes the most is the cases & how their made. Not the powders or how the pressures are measured.
The #1 reason for conflicting data, outdated data or removed/reduced data is the changes in how the cases are made. Every time a mfg changes the font on a case (caliber stampings on base of the cases) it signifies that a change was made in mfg of that case that has changed it's reloaded. Some of the changes (but not limited to) are changes to the wall thickness, base/web thickness, web shape (cup) primer pocket thickness, etc. Any of those changes will effect the case volume, hence changing the load data/powder charge. Some of the minor changes are the addition of a cannalure or base angle/shape/roundness for the automated reloading machines, increase or decrease in the # of steps taken to form/make a case, etc.
A good example of this is what I used to load decades ago. Used to shoot skeet every now & then, used a 20ga. Loaded ww aa cases with ww primers & ww aa20 wads with a load of 14.3gr of greendot powder. My brother calls me last year & wanted to know what I used to use for skeet loads, he wanted to use up a bunch of 20ga wads he had laying around. I told him the load above & a couple of weeks later we're talking about something & he brought that load up. He said he couldn't find it in any of the new manuals so (He's always done this for decades) called alliant & asked them about that load. They told him flat out, DON'T USE THAT LOAD!!!!! He asked them why, did they change the powder? The rep replied heaves no, ww changed how the make their cases.
So when you see older data, don't assume they measured the pressures wrong or they are making the pressures different now or the lawyers say to drop it down, etc.
With the "new" firearms with the unsupported chambers & lite alloys that have come out in the last 20 years alone with the new high energy powders. The mfg's have reacted to the safety issues (stronger webs/smaller case capacity) along with using modern powders that are giving the same velocities as their older counterparts but have less pressure.
I'm not saying that some of the older loads/data was flat out stupidly wrong. I just wanted to point out the thing that changes the most is the cases & how their made. Not the powders or how the pressures are measured.
