Roll works ok for straight wall stuff, but there can be a really fine line between no crimp and buckling casings with seat/crimp combo dies. When I was loading 38-40 and 44-40 I never used the seater as the crimper... lost too much brass attempting it.
For anything with a shoulder I like the Lee FCD.
Yes, .38-40 and .44-40 are thin cases and need to be handled with care and a degree of precision.
For all my loads that require crimping (which for me is all handgun loads) whether roll or taper crimp I seat and crimp in two separate steps. If I don't have individual seat and crimp dies, I back off my die until the case is not engaging the crimp profile section of the die. With .44 magnum and .357 magnum this is just a matter of putting the ring that comes with the dies to switch from "magnum" to "special" under the die's lock ring. Then I seat bullets, adjusting the seating plug down until I've got my overall length right. With taper crimped loads this usually means within a few thousandths of the length given in published data for that bullet/case/powder combination. For roll crimped I like to see the case mouths either halfway up the cannelure on jacketed bullets or just short of the top of the crimp groove on cast bullets.
When all my bullets are seated it's time to adjust the crimp die, whether this means setting up a separate crimp die or backing off the seating stem of a combination seat/crimp die and using it to crimp. I run a cartridge with the bullet seated up into the crimp die, then start screwing down the crimp die until it makes contact. When it makes contact I back the cartridge out of the die, adjust the die down a small amount, maybe an eighth of a turn, and run the cartridge back up into the die. Then I back it out and take a look. I repeat as necessary until I get the results I want. With taper crimp dies, this means a measured dimension across the mouth of the case over the bullet. This is usually .003 - .005 under the nominal case mouth dimension. With roll crimps on jacketed bullets I like to see about half the thickness of the brass pushed into the cannelure (eyeballed measurement.) With cast bullets I like to see the case mouth rolled into the crimp groove as much as possible.
When I think I've got everything right, I measure across the case just below the crimp to be sure I haven't pushed the case out or distorted it with too much crimp.
Another factor that affects handgun ammo quality, particularly with the big revolver cases loaded with slow burners, is the size of your expander. You can't make up for a looser than optimum case to bullet fit by crimping. For the best in accuracy with such loads it's important to have a tight fit on your bullet.
Oh, one other little detail: I get my handgun brass in, usually, boxes of 500 from Starline. When I get a box of revolver brass I go through the entire batch and trim the case mouths. There are two reasons for this. First, they all need to be the same length to crimp consistently. Second, to get a good, consistent crimp, you need a square, sharp edge at the case mouth. Starline brass tends to be very uniform as far as length, but nothing formed by impact extrusion is going to have as uniformly square a surface with the sharp edges that a cut provides.
Patience and attention to detail will help you avoid 99.9% of the problems people encounter reloading handgun ammo. For top notch accuracy and consistency I think the bullet to case fit and the seating/crimping part of the process are the big things.
I may have gone a bit beyond the OP's original concern, hope it helps.
