Just before the Mescalero's attack Rogue (Lon Chaney) says, "They didn't have much ammunition at the Alamo either." The real story is that there were more than enough firearms and ammunition at the Alamo. Before the Texians captured the Alamo from the Mexican Army it had been a military arsenal. Including the firearms brought with them, each man had four rifles each, plus shotguns and pistols.
There were 14-16K rounds of ammunition for them. There were 21 artillery pieces with over 2,300 rounds for them of different sorts and calibers.