You can use the 16 GA since the nails won't be under shear force. A couple issues with 16 GA guns, the nail head is rectangular, you have to position the gun so the nail head runs with the grain, sometimes the nail head will lift a chip when it sinks in. Most 16 GA guns have straight nail magazines and longer nails stick out the bottom, be careful they don't ding the wall since you will be holding the gun straight up and down. Finish carpenters prefer 15 GA guns because the magazine is normally angled and stays out of the way. The round head nail makes a smaller hole and the nail shanks are more stout. The gun tip is often longer and smaller so it gets in tighter spots but 16 GA is fine if that's what you have, the serrated shanks hold quite well.