The only data for Hs7 I can find in the Speer, Lyman, Sierra, Hornady , Hodgdon, Nosler, and Lee books, are for the Nosler 250 gr and a 260 gr in the Lee book. I don`t think this is a good choice for powder in this cartridge as it is quite abit slower then Hs 6 which is widely listed in all books.
The data I did find thugh shows your load of 10.3gr to be a starting load, not a bad place to learn from. If you have a scale I`d recommend adding a 1/2 gr to your charge and see if the soot clears up. You may have to go up a full gr or two to get enough pressure to prevent your dirty cases.
Low pressures, which the 45LC operates at, does`t expand the case mouth and body quickly enough to prevent gas from blowing back down its walls. The trapped gas deposits soot under pressure which is what you are seeing. If you have a Ruger, or TC Contender you can raise the pressure some above the std for the cartridge. I don`t feel this is the best way to prevent this though, If top std loads don`t work, a change in powder would be much more useful IMO. A powder such as Unique, Blue Dot or Herco will give top 45LC velocities within the SAAMI pressures set for the cartridge, and burn much cleaner to boot.
If you are useing lead in place of jacketed bullets the called for start/max charge will vary and data for the proper constructed bullet should also be followed.