Re: Red Dot for 45 Colt in a derringer - Good idea?
It seems to make sense, but in reality may not.
Powder burn speed is to be matched to bullet weight primarily. Lighter bullets use faster powder better and heavier bullets require slower powders to get proper pressure and therefore velocity.
You can safely use Red Dot in a .45 Colt case, but velocities are limited - even in a derringer - and the pressure curve is more of a spike.
Of course, in a derringer, the weight of the pistol is less and therefore recoil is more. One also notes the pressure level is lower, therefore the internal burning temperature is lower and that will reduce muzzle flash.
Used to be in the days of less powders and bigger revolvers, Unique was considered the perfect .45 Colt smokeless powder. (This was before the time of Ruger revolvers that can withstand higher pressures than Model P Colts or even the New Service revolvers.) As a handgun powder, Unique is normally thought of as a middle speed powder. If you have any Unique, you might give it a try and compare those velocities with that of Red Dot.
You might try some loads with slower powders as well, but your hand may not like it as much.
Elmer Keith's book Sixguns discuss a wealthy Alaskan gentleman who carried a pair of Colt SAA revolvers with the barrels removed entirely, using only the chamber as the 'barrel'. The reason for the odd treatment was he carried them in his greatcoat pockets as defense against the unruly citizens of the town in which he lived. I cannot remember the loads discussed, but I don't recall them being especially fast powders for the day.
It is your choice, of course. Proper doses of Red Dot will not hurt your firearm. (Neither will proper doses of Unique or 2400.) Try a couple and see what gives you the best combination of horsepower and recoil abuse.
The 255 grain Keith bullet is just about perfect for .45 Colt. You may want to consider a 200 grain SWC if the recoil of the 255 bullet is more than you like.
Finally: Do report back. I'd like to hear the results.