I have a Navy Arms LeMat. I bought it back in the 90s.
Navy Arms said to use a .451 round ball. When I went to load the revolver with a .451 round ball, the loading lever bent after about the third round. I removed the loading lever and fired the chambers then cleaned the revolver.
I called Navy Arms and they gave me an RMA number. I sent it to them for repair and they sent it back to me looking like new.
Again, I attempted to load the revolver with a .451 round ball. Again, the loading lever got bent! Again, Navy Arms repaired the revolver.
By this time, you are probably asking; did he try to load it again with a .451 round ball. The answer is yes. And, I had some choice words for Navy Arms, who repaired the revolver again.
After getting the gun back, I decided to mic the chambers. They all measured .444 inches! That's a difference of .006" and the loading lever is just a steel sleeve with a rod inside. That explains why it bent so easily.
So, I decided to use .445 round balls as I could not find and that were .447 inches; which would be .003" over the chamber diameter. If you don't remember anything from this message, remember to mic the chmabers and select the size of your ball accordingly!
I use 25 grains of FFFG and the gun is really accurate. Don't go over 3/4 ounce of shot with 50 grains of powder for the shotgun barrel.
Exercise extreme care with the loading lever and the retaining spring. I've heard about that spring breaking and don't want to have that problem.
Regardless, of the manufacturer, I recommend that you mic all the chambers before you select the projectile.