.243 Win. H-380 Loads Decreasing in Velocity with Age

[SAKONUT]

I tested several batches of my .243 Win. 75 Grain Speer Hollow Point loads today. I have always used 41.5 Grains of H-380 with CCI-250 Primers going as far back as the early Nineties.
The rounds I loaded yesterday shot 1/2” groups at an average velocity of 3,174 fps, The rounds I loaded in 1993 shot 1/2” groups at an average velocity of 2,800 fps and printed dead center but 1” lower, the rounds I loaded in 1991 were identical in velocity to the 1993 loads but printed 1-1/2” lower than the newly loaded rounds.
The recorded speed that I put on the box of the loads back in 1993 & 1991 was 3,180 fps

Here is my question; Is it common for older reloads to chronograph slower with age?

 

[Coyotefurharvester]

Yes especially if the neck cracks when fired(just something to watch for on old reloads).

 

[ronemus]

Naked bullets in contact with a clean brass neck will bond, which can affect velocity (and pressure) by unpredictable amounts. It is good practice to seat bullets in old loads slightly deeper to break the bond; that will make the loads more consistent and avoid pressure spikes.

 

[SAKONUT]

The cartridges were all new unfired brass before loading them, there were no cracked necks all of the fired brass looks great!
I will definately try seating those older rounds from 1991 about 4 thou deeper before I go back out just to see if that changes anything!