Gerry, when it comes to loading flat base cast bullets into quite large cases, like your 33 WCF, strange as it may seem, the actual calibre of the case is not too important. That is, even Lyman in there famous Handbook of Cast Loading, will group calibres which are of similar size. Even that old 'bible' of cast loading doesn't show the 33WCF.
With cast bullets, especially non gas check, maximum loads are not adjusted as to pressure for your rifle, but max loads means the maximum velocity the cast bullet can be driven, before pressure starts to eat past the bullet, resulting in patterns, instead of groups.
So, to get a load for your 33W, we just look at similar sized cases in the Lyman cast book.
With a 348 Win, 20 grains of 4227 should be a good starter.
A 358 Win starts out at about 12 grains of Unique.
The larger 35 Win with 250 grain bullets, starts out at about 17 grs. of Unique.
In short, Unique will be an excellent, never fail, powder for flat base lead loads and about 12 grains would be a good place to start. You could then increase the charge, as long as accuracy was OK.
4227 is also an excellent powder, and something like 18 or 20 grains may be a good starter.
When working with fast powder in large cases, always be very, very sure, that you do not double, or even triple the intended load.
I have never used Trail Boss, but I believe it's advantage is that it is so bulky that you can not get a dangerous load in the case, so if you wanted to eliminate the danger of getting too much fast powder in the case, you could always go to Trail Boss.
Bruce
