I don't know if its HC or not, but I use a file to cut simple molding lines on the fore end as well as the relief line along the toe to wrist line of the buttstock and on the cheek piece. Draw out a line and drag the edge of a halfround file over it lengthwise. Go slow at first, while you are just scratching the line, then when it becomes a cut line, you can increase the depth of the cut more quickly, once you are "in the groove"
. I won't say you can't get a crooked line, but the length of the file makes it easier to stay straight. If the file is tapered, it will make the initial cut a little trickier, but it will also allow you to "fade" the line out toward the end. You can also modify the profile of the cut depending on how you hold the file and which side of the half round you use "up or down". Obviously, other file shapes can be used as well. The triangular file makes a very nice, simple incised line for example. This works for straight lines only -- but it eliminates a lot of the work; if you need a curlicue or curve to terminate, then you have only a very little "carving" to do freehand.