BB, here is a photo and text copied from a post the man himself, Nate KJ, posted 10-12 years ago on this forum. (I kept this for my own archives.)
Nate does business as Steve's Gunz (https://stevesgunz.com). Here's a link that will give you several "hits" on the topic.
"As some of you know, I specialize in these CAS leverguns and have been for the last 18 years. Here are some things that I have found.
As for the feeding problem with these rifles, all our leverguns are length and bullet shape sensitive to some degree. Like semi-auto handguns, they can be picky about what they will run and the faster we try to go with them the more often these problems tend to show up. I think one of the reasons folks like the 66&73's is they are less ammo sensitive than the others. Someone mentioned that these 38-357 guns are designed to shoot the 357mags and they do better with the longer 357m rounds. That`s just not the case. What Rossi, Marlin and Winchester have done with these 38/357 guns and to some degree the 44sp/44m guns is compromise the timing to handle both lengths. This compromise is like a combo tool compared to a tool that is designed to do one specific job. The combo tool will never do as good of a job as the tool that is designed specifically for the job. That is one of the reasons marlin came out with their cowboy comp. in 38 only.
It's not just an OAL issue. It's an OAL and bullet shape issue. The very best feeding cals are the bottleneck cals these guns were originally chambered for. You have a little bullet going into a big hole funneling down. Make ammo that replicates this as much as possible. An elongated style flatpoint bullet without any external driving bands in a 38 case works best and that is because it is much easier to lengthen 38`s as compared to shortening 357`s.
When making these long 38`s keep in mind, just because a lead bullet has a crimp groove, that doesn't mean you have to use it. You can seat the bullet out long and crimp right into the side of the lead. A good place to start is to seat a RNFP bullet out to about 1.5 OAL or slightly longer.
Here is a good example of a lead bullet set out beyond the crimp groove in a 38 spec case.
The other thing to consider is no two guns are alike. When the parts for the guns are made, the maker has a nominal size for each and ever parts that goes into the gun. But they will accept a part that is plus or minus a few thousands. Once all these various parts are assemble every gun will be slightly different. This is called stackup.
I have had consecutive serial numbered gun here. One would run even on empty brass, the other would not run on anything without some tweeking. If you have tried different styles of ammo the gun may need some timing work to run right."
--Nate Kiowa Jones