Thread: Old Data and Load Variations. Traps for New Handloaders

Greetings All,
In another thread I talked about my simple methods for validating load data. The cartridge was the .260 Rem with the 140 grain plus projectiles and AR2209 powder. I have started a new thread to stop cluttering up the other and to possibly reach a wider audience.
To me there was a glaring difference between the max loads for the 142 grain Sierra SMK and the Hornady 143 grain ELDX. For the former the quoted max was 44.5 grains of AR2209 for 2735 fps and the later it was 42.9 grains of the same powder for 2,759 fps. To me the projectiles are very similar so loads and velocities should be as well. I have banged on about the speeding up of AR2209 a little after 2,000 so I hunted back through my old load data. The Sierra projectile data goes back to at least late 2,000 and likely to 1997 or 1998 after the .260 came out so this is old data. The 143 grain ELDM did not exist then and did not for some years after so its data is newer.
So why does the ELDM need 1.6 grains of AR2209 less to reach a little more velocity? The speed of AR2209 has definitely changed as I found in a paired chronograph test a few years back. Loads needed to be reduced by1.5 grains to give the my original velocity with the new batch of AR2209. I am not bagging ADI or Hodgdon and definitely not AR2209 which is a great powder in my opinion improved by an increase in speed. Hodgdon does a great job producing and upgrading data tor their and ADI powders but it is still our job as handloaders to spot these little gremlins. My experience is that most powders are pretty uniform but all of them vary over time and from batch to batch. This also applies to other components so how do we keep on top of things?
My system is to chronograph a reference load with new batches of components to detect changes in velocity and pressure. Generally this yields no surprises but sometimes it does and my standard load can be adjusted.
Lets be careful with those loads.
Regards Grandpamac.