I guess I didn't explain enough in my post.
I'm not suggesting you use W780 in .223 Rem.
I just wanted to make sure the slow powder option was pointed out. For .223, I probably wouldn't go any slower than the 4895/4064/W748 class of powders. (For me. My loads. My rifle.)
Unclenick, Charlie Sisk later points out that his testing showed a great variety of loads to cause secondary pressure spikes, including factory ammo and 'average' bullet weights (not just light stuff). Without using heavy-for-caliber bullets, there is no good way to completely negate the chance of secondary spikes.
The only methods proven to work are:
Chopping the barrel to a point that the bullet exits before the secondary spike hits.
Using pressure testing equipment that 99% of us can't afford, or can't justify purchasing.
Although I wouldn't mind discussing this a bit more....
I am usually a bit of a Safety Nazi in the reloading forum; so I'm going to side with Unclenick, and suggest avoiding slower powders with light bullets. (I also don't want to drag this thread any further off topic.)