It's probably a combination of little things adding up. The one thing I've noticed in these guns is little or no throat and a snug chamber.
The no throat has the chamber ending and the rifling starting , that's why the rounds will fit the chamber gauge but will not fit in this gun. Try to find a bullet similar in profile and diameter to the factory bullets that do function. I have a tight 45 acp that will not chamber any ammo loaded with a bullet over .451 ". Sized .452 and it's a no go, size that same bullet .451 and they will function.
Another solution is to have the barrel throated , this will give you some more room to work with.
Gary