FWIW, a .410" diameter round ball cast from hardball alloy with pass through the fixed full choke of my mossberg 500e without incident. I have shot 3 and 4 ball loads over I4227, at modest 1,100 fps speed.
I am working with both 0.375" and 0.410" roundball loads and hope to have them sorted out fairly soon. The 0.375" are showing the most promise in my 410. It appears that keeping the roundballs centered in the bore is the key to accuracy.
BB