I haven't tried denim but last spring I sewed seams of boat tarp canvas with my 401a. DH had to manuever the lengths of canvas but my 401 plowed through easily. I imagine if it could sew through 4 thicknesses of that type of canvas it could sew through denim easily.
You know, I used a new denim Schmetz needle the other day and it looked rounded at the tip. I will have to look at my other ones.