This is about three years later than you asked, but I reply in case someone else has this question. I'm not positive this is the answer, but I believe it to be so. The gun was wet from the rain and wouldn't fire. So, he poured sand in the gun to dry it out.
shareIt is said that he tried not to spread his-own blood around himself. Ashes functions adsorbing bleeding to some extent.I am not sure if it is correct, but it might origin the way of commuting suicide in Army Mr. Kasahara writing script had worked,in fact, putting a gun into throat(not putting to head) is the right way to do in Army, because as ordinary soldiers did not carry hand-gun but long-rifle, they had no choice but to put it into mouth with pulling trigger by foot-finger, Mr. Kasahara makes him do the same thing like Army-method, even though it is the hand-gun, due to obsession or considering his-own experience.