I have been shooting a .357 1894 Marlin in Cowboy Action Shooting for over seven years. I shoot .38 special reloads (my own) in this rifle with no problem. Now having said that, Marlins can be very sensitive to ammo length when run at competition speeds. Our Marlins like the ammo to be loaded to 1.5 inches COL or longer (I actually load to 1.51" COL). At that length they function beautifully at competition speeds. .38 ammo that is "normal" length will sometimes cause a hiccup that manifests itself in a need to back off the lever slightly, then close it. This isn't a problem when plinking, target shooting, or even hunting, but it's frustrating as heck in competition where you are levering as fast as you can acquire a target.
Bullet shape can also cause a similar feeding issue (and a SWC is a particularly difficult bullet for a lever action to feed), but each rifle is different. Our three Marlins seem to be indifferent to bullet shape; as long as the ammo is 1.5" or longer they will feed it. I use RNFP in competition.
As far as feeding goes, though, any lever action rifle is sensitive to ammo length. The Winchester toggle-link design (original 1860 Henry, 1866 Winchester, and 1873 Winchesters, and their Italian clones) is somewhat less sensitive than the Marlin, but that is a relatively weak-design action. The Winchester 1892 (and current Brazilian and Italian clones) is a very strong action (actually stronger than the Marlin) that is even currently produced in .454 Casull and .480 Ruger chambered rifles, but it is as sensitive to ammo length as the Marlin. My .357 Chiappa '92 likes the same length ammo that our Marlins like: 1.51" RNFP. I've got a .454 Casull LSI '92 that I also shoot .45 Colt in, and I had to custom-tune the .45 Colt ammo length for it to function well. The Winchester 1894 is a strong action, but it was originally designed for rifle cartridges, and can have some weird feeding failures when the rifle design is modified to function with pistol cartridges. I have very little experience with the current Henry Big Boy rifle. I know some folks that have the rifle, and they either love it or call it a "jam-a-matic". From this I would hazard a guess that the Henry Big Boy is very sensitive to ammo length. All I can say for sure is that the Henry Big Boy is very rarely used in Cowboy Action Shooting.
All in all, I prefer the 1894 Marlin action, as it's as reliable as any (and better than most), very strong, and very easy to clean. Plus, since the Marlin is a side-eject, it is easy to put a scope on the rifle.
My ammo chrono's at around 750 fps out of my pistols (7 1/2" barrel), and around 900 fps out of my Marlin (24" barrel). It's not just the barrel length that increases the velocity, but also that the rifle doesn't have the "barrel-to-cylinder" gap that a revolver has. I would
guess, since you have chronographed your ammo from a 2 1/2" revolver barrel, that you'll see a velocity of somewhat more than 1000 fps from a rifle. As far as leading, that should be no problem unless the bullets are very soft. I don't have a leading issue in the .454 until I get over 1200 fps with the .454 Casull rounds and hard-cast (non gas checked) bullets. At velocities over that I use gas checked, or jacketed, bullets.
I guess what all this boils down to is that, in my opinion, you'll be happiest with the Marlin!
