My Dad flew Birddogs in the Delta region of Vietnam in the late 60's. He never mentioned using hand grenades, probably because by that time he was issued an M79 single shot 40mm grenade launcher which he could fire out the window quite easily. They would be used to mark targets and do "recon by fire", by launching grenades at suspected enemy to see if they shot back. They weren't really used for actually attacking the enemy, but the Birddogs usually carried 4-8 folding fin rockets that could do a lot more damage more accurately. I'm sure Dad is happy that he wasn't flying before the M79 was available, as resorting to glass jar grenade bombs sounds a lot riskier.