Yes, the extra unrifled area ahead of the shorter cartridge in the cylinder is what I'm referring to as freebore. Results and opinions are mixed on this, but common sense dictates that the longer the bullet has to travel to the rifling, the faster it accelerates, and when it slams into the rifling at a higher speed, there has to be some stripping before it grips the rifling and spins up.
Muzzle flash depends greatly on the powder being used. A slow rifle powder won't burn completely in the ten inch barrel, and can cause flash from unburned powder. Most all powders will give off a muzzle flash though. Even with the proper powder, even though the powder may be completely burned, the gases created have used all the available oxygen and are still combustible in themselves. They are heated past their flashpoint, and when the projectile clears the muzzle, and the gases come into contact with oxygen, they flash and burn.
The recoil of .45-70's in this thing is somewhat comparable to a big-bore black powder pistol. A big push and plenty of "kick", but not sharp like a conventional revolver cartridge such as the .475 or .454. There's a lot of room in that big case and pressure builds up slower, but it's still not a problem to safely propel a 405 grain cast bullet to over 1500 fps in the 10" barrel. I was definitely spooked the first time I shot mine, but it's certainly no worse than midrange .500 loads out of a compensated X-frame, or heavy .44 mag loads out of a SBH.
The original FF black powder load propelled a 405 grain bullet to 1325 fps, or a 500 grain bullet to 1250 fps... from a
rifle barrel. I can safely top this by 200 fps in a 10"
revolver barrel!
Of course, even this pales when compared to velocities that can be achieved in a Marlin Guide gun or other modern .45-70, but still...