Ditto to everything Bruce said.I use H110 and W296 (same powder)exclusively for magnum loads.Most of those who complain about this powder are the ones who really don't want to shoot a magnum.They simply like to see the word "magnum"roll marked on the barrel.
If you want light plinking loads,H110 and W296 are not what you want but I don't think 275 and 300 grain bullets are what you want either.With bullets of that weight,it's assumed you want power otherwise lighter bullets make much more sense.
Ever since the heavyweight bullets became popular in the sixguns,the load most mentioned in the way of 300 gr cast bullets in the 44 magnum is 21.5 gr of H110/W296.It's definately hot to trot and I wouldn't use an extensive amount in the Smith revolver.
Anytime one uses bullets for which there is no "specific data for that particular bullet",a certain amount of extrapolation seems inevitable....likewise in this case.Each bullet is different and an equal measure of experience and common sense are needed.
Lyman#48 shows.....17.7gr of H110 for a starting load and 18.5gr for a max load behind their 300 gr 429650.......Pressure with that max load is stated to be 37,900 cup.Velocity is 1036 fps from their 4 inch vented test barrel.OAL is 1.700.
With their 275 gr bullet(429640),they don't give data for H110.They do with 2400,AA9 and N110.
I personaly prefer to use data for a specific bullet when I'm loading pedal to the metal but there are those who do otherwise.I'll give you some data out of a 2006 Winchester manual for W296(same powder as H110).
270gr Speer GDSP....21.5gr....1421fps...37,700 cup
280 gr Swift jhp.....20.5gr.....1342fps...36,100 cup
300gr Hornady XTP.....19.0gr....1325fps....38,800cup
These are jacketed bullets and needless to say,pressure and velocity will NOT be the same with your cast bullets.Jacketed bullets do indeed build more pressure when all things are equal because of the friction for the most part.Seating depth,bearing surface,etc have an effect on pressure.You're on your own as no one will promise the results.
Hope this helps.