Manure
Manure is usually a prime ingredient in the making of mushrooms. Your friend seems to have covered that already. Being a rifle shooter mostly,I shoot a pistol enough to keep the bad guys from getting to close,Mushrooms are the product of bullet construction,impact velocity and resistance imparted by the tissue impacted. Some bullets have polymer tips to help aid in bullet upset,some have hollowpoints,others soft points. Pistol bullets are mostly built along the same lines. As for the failure to expand,your friend should count himself lucky that it did not. I would have recovered the said projectile and concluded that the projectile had failed miserabley. If it was a hollow point it may have been the result of being clogged by the very fine Italian leather of his shoes. If it was a SWC design then it did what it was basically supposed to do which is cut a hole. Like I said,I would regard this as a failure and would hence forth seek another projectile which would meet my criteria (sic) to expand inside the target. I like holes that have no bottom. Thru and thru's bleed alot better since they have two sides to bleed out of. Oh man,I cant beleive I was the first one to see this one. Poor guy.
If someone supplies the manure,given enough time a mushroom will surely develop. Oh boy ,,,,,,,,,
Democracy is two wolves and a lamb voting on what's for dinner. Liberty is a well armed lamb contesting the vote." - Benjamin Franklin