I recently purchased an original Ballard Pacific in 40-85 and my first trip to the range fireforming 9.3x74R brass ended abruptly after 6 rounds when the sear spring broke.  I am back on the ready line and went out today to continue fireforming with a light smokeless load.  Attached is a picture of a 10 shot group at 50 yards with a silver blade front and a Lyman tang.  Needless to say I was very happy.  I also loaded the six previously fired cases with holy black and paper patched bullets.  All I can say is "OUCH"!  The bore riding bullets shot poor but the dual diameter I have for other rifles was fair but I only shot a few and my shoulder called timeout!  Lessons learned were that the 9.3x74R cases extract as good as the BACO cases formed from 40-90, that the gun will shoot when I get a good load, and last I think this might be a smokeless only gun for awhile.  My 4th Edition of Lyman Cast Bullet Handbook lists many loads for the 40-70 SS and I have two rifles in that caliber that have shot excellent with both black and Buffalo Powder.  Now I am going to try smokeless in the 40-85 with 350 grain bullets and planned on starting with the maximum load shown for the 40-70 thinking that the much larger 40-85 case would produce much lower pressure.  Is this a good assumption?   The load for 5744 shows 19,000 psi in the 40-70.  Tom

Rifle picture...

To the OP; did you clean the bore between shots with paper patched black powder loads? If not, try shooting over a clean bore. As for smokeless powders I would not chance destroying a rifle that nice, too many possibilities for damage going that route. Your rifle, do as you please but my money is on black powder for accuracy when it comes to the low pressure loads required for that rifle.

None of my Ballard rifles have seen BP in the several decades, and thousands of rounds fired while I have owned them. As Lee mentioned, if you keep the pressures down there's no reason they should ever have a problem.
Your thinking about the .40-90 Ballard having less pressure with .40-70SS loads makes sense. Still not sure I'd start out with max loads for the .40-70SS though. I'd sneak up on it, and start a bit lower. I've never used 5744, so wont comment on loads for it.

Tom,
I have a couple of rifles on either side of yours, a 40-70SS and a 44-85 Wesson that I load with 5744.  Both have favorite bullets that perform well to 550 yards but I haven't found a favorite for either that like anything much beyond that.   
The 40 gets close to 20.5 grains to push a 455 Nasa -1150 fps, and the 44 gets around 25.7grains to push a 525 grain Creedmoor at 1230fps.  (I have set these both up with a pressure trace strain gages to get actual pressure data- just haven't had the time to collect it yet).  Recoil is pleasant for each and accuracy has been very good.   
I have struggled with both of these trying to get comparable accuracy using black and the felt recoil of the 44 with black is brutal.
Good luck with your project.
Greg

I would have placed that crescent but plate into my shoulder. Ouch, those bruises look nasty
Oh, nice lookin' rifle.

That's not a schuetzen rifle Tom. Best keep it on your shoulder, not the upper arm.