Search:

Sorry 223nut. Not in a position to get to my reloading data at the moment. Will look when I can.

Better clarify my own post here.
I could get it (trail boss and 55gn BTs) subsonic but it was not accurate. (2" at 50m)

Thanks for that. I didn't realise it had anything to do with the powder burn rate. I thought it was purely down to too lower load density regardless of the burn rate.
From that last thread I read it...

Just found this thread.
http://handloads.com/forum/showthread.asp?topic=5&thread=2473
Interesting.

Kscott. Be careful with load density (the proportion of powder in the case). If there is too much air space in the case you can (apparently) run the risk of detonation. That is the powder lying flat...

Because you can.

Had a bit of a play with trail boss in the 223 but couldn't get it to shoot subsonic. Didn't really preserver though.