AA 8700, H-870, and WC-870 in my opinion are all the same powder which was developed for spotter rounds based on the 50 bmg case shortened. It has a very slow burn rate suitable for the largest magnum cases with the heaviest for caliber bullets.
The AA data book shows loads for it with some of the large caliber straight wall cases but I can tell you from experience that the pressures are way too low to consume the powder and it leaves a lot of unburned powder in the barrel and the case. 
Since this powder is still available as surplus at about $7.00 per pound I have learned how to used it in BPC type cases by duplexing it with a kicker charge of faster powder which pushes the unburned powder out of the barrel and allows free chambering of following rounds.  Used this was it produces black powder velocities but does not require the cleaning as does black powder.  I used such a duplex load at the Quigley shoot in a 45-70 and did very well.  My load produced very low extreme velocity spreads in the teens which is very good for any powder.

I have also duplex loaded it in bottle neck cases like the 30-06 and gotten excellent cast bullet performance with it.  8700 is normally too slow in burn rate for the 30-06 even with 220 grain bullets but when duplexed with a kicker charge of faster burning powder it gives very good accuracy at quite high velocity for cast bullets.
The powder burn rate of the kicker charge is kind of critical in that if too fast it can raise chamber pressures more than  wanted and if too slow does not give good effect in shooting the barrel clean.  Powders I usually look at for this will be on the burn rate chart starting at about 2400 and ending at about 4198.
I just went to    (You need to Login or Register to view media files and links) to see if he has any WC-870 and it looks like not right now but if you look at the last two powders on his list and their application you see they are similar.  I also use a lot of the one right above those two 7383.  The 7383 has the burn rate of !MR 4831 but has a higher bulk density which means you cant fit quite as much by weight of 7383 in any case as you can 4831.  This works out quite well for heavy for caliber cast bullets loads at quite high velocity in many modern cases. For instance I get 2400 fps with a 220gn cast bullet from the 308 Win with excellent accuracy.