Vegeta clearly needed a lot of energy for Galick Gun
Gokus Kamehameha was stronger as Galick Gun but i took almost the rest of Gokus energy.After Vegeta got hit,he was almost down,barely able to do shit.The only thing he was able to do was to create the orb to transform him into his Monkeyform to get A)Stronger and Faster.And B)Refresh his Energy.
Pretty much everything speaks for the fact that vegeta cannot use his galick gun several times in a row,before he has not recharged his energy