Re: tempature sinsitive powders
Depends on how long you let it heat soak. A warm chamber still takes a couple minutes to warm the powder up a significant amount. If you drop the round into the chamber, and fire within 10-15 seconds or so, that's not enough time to heat the powder up enough to note a appreciable amount to effect your muzzle velocity a significant amount.
There are f-class shooter out there that will chamber the round, and if they don't fire within' 30-45 seconds, they will remove the round, and allow it a chance to return to ambient temperature before they go to fire it again. However, in f-class, they are getting their rifles a bit hotter than most of us are.
Branden