I'll set it up. T/C Encore-454 Casull bbl. hot 45 Colt loads using WW-296. Uncrimped (my problem?) 240 gr Horn Mag HP and CCI-350 Mag primers. When I fire them, I get unburnt powder between case and chamber wall (to within 1/10" of the rim!)with a discolored case. I would have to clean out the chamber to put another round in. I also have to scrape the powder residue off the case with my fingernail. I'm wondering if I crimp the cases, it'll give the powder more time to burn before the bullet takes off...what's happening?

W926 needs a very heavy crimp. Your freebore by firing .45colts in a .454 may also be causing some of the powder to blow by.

I concur with Fred. If you chronograph those uncrimped loads, I'll bet your shot-to-shot variation is all over the place!

H110/W296 typically needs a heavy crimp to burn properly. As I understand it, the crimp slows the release of the bullet for a sufficiently long time that pressure and heat can build to completely and efficiently consume the entire powder charge which in turn creates the gas volume necessary to provide the performance expected. IME, failure to use a crimp with these slower burning powders will result in substandard performance with characteristics such as you describe. The same will happen with 2400 (even with charges which are on the low side).

The key to accuracy is often a consistent crimp which is dependent on properly trimmed cases of very consistent length and properly adjusted (and secured) seating dies.

Great..thanks for the advice. That explains the crappy performance with the 2400 loads I shot the same day.