Without seeing the rest of the rifle for perspective, it's kind of difficult to tell, but I would tend to believe it needs to be filed smaller. Most pulls (wedge keys) had fairly small heads, and the shafts were pretty thin as well.
I don't know if this will make sense, but one way to slant the heads is to use a piece of steel stock that has an angle filed on the face, so it looks like a flat chisel. If fact, an old flat chisel would probably work... Anyway, clamp the pull and angled stock in a vise, with the pointy end resting on the bottom of the pull head. Gently tap with a small hammer and the head will slant down. The reason for the angled stock is to make room for the head to slant. That's probably confusing, hope it makes some sense... I should probably post a photo...
Ed