Both versions of the P-39 (I thought the later was MUCH better???) seem to land countless hits on planes with very few "killworthy" hits.
I unloaded a dozen into the b-24 drone, and only popped a gear, a flap, and a gas leak. Land it by the pilot and you can get a kill, but I landed at least 2-3 on the P-51 drone with no noticable effect before the 4th popped the wing off.
Note the p51 example might have caused a pilot wound, I couldn't tell, but it sure didn't damage much else!