The receiver on these guns is very similar to H&R, with some parts being almost the same. Check the FAQ's for ideas, but if the lifter is good and the pin protrudes far enough, the only other thing to check is the hammer spring....that is if it previously shot well then began this.
If it never shot well and had FTF's, it still would go back to the basics listed in the FAQ's.
My nephew's Rossi had a broken firing pin, I could not get one so I had to make one from some drill rod....
Ben