I have a hard time seeing the need for 405's at 1800 FPS for target shooting, or anything else for that matter. I have no doubt your buddy was being beaten to death.
As far as leading goes, it seems to me that leading in the last few inches of the barrel is generally a lube problem and given the long barrel of the BC I'm not surprised the bullet runs out of lube before it reaches the end.
Like shot1 I use 5744, 30 gr gives me about 1300 FPS. 5744 is a very bulky powder and was designed to dulicate original loads in older blackpowder cases. It's bulkiness does a good job of filling the cases, giving consistant ignition and reducing the possibility of double charging a case.
Another powder that works extremely weel in black powder cases is Trail Boss. It's even more bulky than 5744, 14-16 gr are all that's needed for a 405. It's so bulky, a standard container that holds 1 lb of any other powder will only hold 9 oz of TB. 16 gr might give you 1,000 FPS or so, it's an easy shooting charge with very mild recoil. If you want to reduce the recoil even further get yourself some 150 gr Collarbutton bullets from Western Bullet Co. These pills resemble overgrown air rifle pellets and when paired with TB you'll have a very mild round.
That's what makes the .45-70 so great. It's easy to load for and can be made to do just about anything. I'm sure you'll enjoy the bejeesus out of yours.
GH1