Check the lens first, It's not uncommon for a lens to front focus. Sometimes it a characteristic of the lens and working aperture.
Tripod, shutter on bulb, frosted tape or ground glass at the film rails not the guides.. With the lens focused on the GG then check the distance scale.
The hard stop in the barrel doesn't mean the lens is actually focused properly and once infinity is found, the focusing ring or barrel can be adjusted to agree with the image.
Using something like a 5X magnifier can give a more accurate image too.