Gmbailey, cartridges for single-shot rifles don’t need to be crimped. Seat the bullet as far out as you like. Ignore the cannelures, altogether. In fact, conventional wisdom is - crimping bullets for single-shot rifles is bad for accuracy.
Everything else being equal, longer cartridges have higher performance potential because they have a larger powder space. The farther “out” the bullet is seated, the more volume there is BEHIND the bullet. The hand loader can put more powder into the case. More powder makes the bullet go faster.
But wait, there’s more! All things being equal, a larger powder space does another thing - it LOWERS pressure. This little benefit makes the whole thing work. Life is good when the laws of thermodynamics become your friend.
Put it all together: load a longer cartridge, that holds more powder, which results in higher velocities, at acceptable pressure levels. As a hand loader, that last part there is REAL important to understand.
However, there are some cautions. There’s some things you’ll need to check out first. Skills needed in determining how long a cartridge you can load. Considerations. Such as - the distance between the bullet and the lands in your rifle’s barrel.
If you don’t know how to do all that stuff, you need to research it, cuz I don’t have time and space to explain it all here and now.
I don’t know about Handi-Rifles, but I have a number of Contender barrels and I can say that Thompson-Center is VERY generous in it’s barrel dimensions (some might even say TOO generous). In other words, you can seat the bullets as far out as you want. To the point were the bullet is practically falling out of the case mouth - and still not be touching the lands.
A longer COAL can transform cartridges like the 7-30 Waters and the .375 Winchester. I wouldn’t be surprised if it did the same for your .444 Marlin.