Tweak some recipes and stats of homemade guns, add m2 rifle modification

Should be ready for commit, but if anyone sees anything that needs further tweaking, let me know.

The blunderbuss in particular has received a large buff in the form of actually having the potential to hit a target. This should make it somewhat more useful, although it was an excellent noisemaker previously.
OK, the 2x4 is sufficiently beneath this line that Git didn't notice.  (Therefore I didn't either.)