Leading question

[GH1]

 Yesterday I took my Marlin 1894 .357 to the range, along with my Taurus Model 65 .357. I wrote a detailed account of it on the Marlin Lever gun forum here.
   Anyway, both guns were shooting the same ammo, a 158 gr SWC BB from Friendswood Bullet company over 5.5 gr of Bullseye, sized to .358.  200+ rounds through the Marlin left very little leading, while 50 rounds left quite a bit of leading in the Taurus.  Why is that? 
GH1

[Nobade]

First thing to look at is the relationship between the cylinder throats, barrel groove diameter, and the bullet. The bullet needs to be a firm thumb press into the cylinder throats. This in turn needs to be the same or bigger than the barrel's groove diameter. If the bullet is too small for the throats, gas will blow past it and lead the forcing cone. If the throats are smaller than the barrel, gas will blow past and lead the whole bore. Either way it won't shoot all that great either. This is the first thing to check.

[GH1]

Are revolvers more prone to leading from the cylinder/barrel gap?  Does a large gap worsen the problem?
Wouldn't it also stand to reason that .38 rounds fired in a .357 will lead foul due to the shorter cartridge length?
I think I'm starting to get a handle on this leading business.
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[GH1]

Over the weekend I did some more shooting, this time with 158 gr SWC bullets from Tennesee Cartridge, over 11.2, 12.2, and 13.5 gr AA#9 and experienced virtually no leading.  Perhaps the more powerful AA#9 privided more obturation than the Bullseye did.  In any event, I think I found a combination that works. Now I just have to play with loads for accuracy.
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[Lloyd Smale]

slow powders give a cast bullet a slower push through the forcing cone and dont deform bullets. they also in many cases burn cooler. Idealy a cast bullet in a revolver should be shot with a powder that gives peak pressure when the bullet is about half way down the barrel. bullseye is a great powder and i use it alot but mostly for plinking loads. 5.5 grains in a 357 is going to give a bullet a pretty big slap. If you loaded down to about 3 grains id bet that leading would go away and your accuracy would improve.

[GH1]

I think what I'm going to do is use the Bullseye for my .38 loads & stick with the AA#9 for the .357 rounds.  I tell you what, I could sure feel the recoil difference between the Bullseye & the AA#9, both in the pistol and in the rifle. If they shoot as good as they feel I think I'll have a winning combination.
GH1