Big order.   My own experience is that a chonograph is the most useful load development tool.   Various powders will like different amounts of compression.   Swiss 1.5 Fg less, Goex FFg more.   I have never found any improvement on the load from using a wad, however, others swear by them.   
     Alloy -- most find that 1:30 is satisfactory, some use 1:20, which is not much different.   Most don't like antimony in the alloy.
     Lube -- I use a lube composed of beeswax, lanolin, and Mobil One motor oil.   SPG will be fine, and very similar.
    Bullets -- I have done some competitive shooting with TD 45-70 and find that for MR, 400 gr bullets of 464 diameter will work - depends on the rifle.   The 400 gr bullets will not upset satisfactorily, but undersized 500+ gr bullets can be used, and will slap the snot out of you in a TD.
   This is not the total synopsis of my ignorance of the subject, but a good sample.

CHRIS
RGChristensen

   Generally you get the best results with as-fired cases, with the bullets seated loosely in the case mouth.  This is a little problem with the 45-70, as you are stuck with a SAAMI chamber, which is somewhat loose.  Loading with the bullets seated firmly into the leade will help center them up.

CHRIS
RGChristensen

this will mostly be for the new .45-70, a pedersoli bodine rolling block w/34" barrel.

i have Lots of bullet flavors on hand, but almost all are #2 alloy and not bp lubed.  until i begin casting, the bullets i'm using are 20:1 chey-cast, 500 grain spire points.  i've used them with good results with smokeless, they're already bp lubed, though i also have my own homemade smokeless and bp lube blends.

(You need to Login or Register to view media files and links)

i've got lotsa goex black in 2f and 3f.

i have both fed 210 and 215m primers.  from my stash of starline brass, i've set aside 100 cases with flash holes drilled and deburred with a #41 bit.

bullets are seated firmly with a redding comp die, no crimping.

i have a chrono and i know about working up loads.  i initially just wanna build safe cartridges, not necessarily the most accurate - that "fun" will come later.  

my concern is the constant warning i read about no air space 'tween the black and the bullet - and as we know, this is just the opposite of smokeless.  

so i gather the compression thing can be from nearly nil to whatever it takes to make an accurately consistent round.  

if the compression nil to a "tad", would a compression plug be required or can the bullet seating take care of a .030" - .062" amount of powder compression?

i guess i'm more or less on the right track.  thanx for all yer responses and help.

If your replica has an 18" twist and you plan on target shooting, get a mould for a bullet of at least 500 grains; 525 to 550 is even better.  An excellent starting point is the Government bullet, Ideal 457125, or a custom version of the same.  Another bullet that you can scarcely go wrong with is the 550 grain Creedmoor formerly made by Paul Jones and copied by a lot of other custom mould makers.  Hold off on specialty designs like Postells, Moneys, Schmitzers and other exotica until you see how your shooting goes with the good old standbys.

For fun shooting with occasional excursions to 300 or 300 yards, another go-to design is the Ideal 457124 for the Government carbine load.  The US Army spent the equivalent of 100 gazillion of today's inflated dollars designing and optimizing the .45-70 with these two bullets.  More RTD&E than any gun company or individual could ever do, so obviously these will be easiest and quickest to get good loads with.  The Schmitzer I tried worked OK in practice but kind of fell apart in a match for me. YMMV, of course.

Put your bullet into an empty unsized case, carefully put the assembly in your chamber and close the breech.  Carefully extract it and note bullet protrusion and slight rifling marks on the nose and front band.  Subtract protrusion from bullet length and this is your seating depth.

Drop tube in powder so the column height plus the wad is that seating depth.  Shoot these loads, note results, and start adding powder, 3 gr at a time, compressing and shooting until the groups shrink to the optimum.  For me, this works out to 63-64 gr Swiss 1-1/2 or 66-67 gr Olde Eynsford, behind the Paul Jones Creedmoor.  Slight compression for the Swiss, somewhat more for the OE.  People I shoot with and many I read about are loading around these numbers, so they are a good starting point.

Use SPG lube and a blow tube between shots.  Take careful notes.  BP loading is more "nuanced" than smokeless, but not witchcraft or rocket science.