.380 reloading Question

[molonlabe]

Having reloaded a lot of pistol ammo over the years I came across a problem that stumped me. I recently reloaded 100 rounds of .380 ammo that I collected over the years. I used a 95 gr LRN behind 3.1 gr of bullseye with a Winchester small pistol primers. I chronographed the load at 940 fps +/- 5 fps. I wanted to push it a little more so I increased the powder to 3.3 gr and loaded 6 rounds and they clocked 911 fps around +/- 5fps. I fired the 3.1 gr right after and they clocked at 940 fps. Normally I would attribute this to unburned powder but Bullseye is one of the fastest burning powder. This flies in face of everything I would expect. I am tempted top drop the load to 2.8 gr to see what happens.

Anyone have any ideas? This is the first time I reloaded such a small capacity case I have done tons of 9mm.

 

[John from MD]

Bullseye is a fast burning powder but there are other considerations that could make this happen. One is, and I suspect that is what occurred here, that the additional powder caused compression of the powder into a slug. When this happens, it actually slows the burn time and, since the barrel is short, some unburned powder is ejected.

To prove this out, buy some cheap sheets and lay on the ground in front of the pistol starting from 3ft from the muzzle. Unburned powder will be found on the sheet if this is the cause.

Regards,

John