49ers’ Ronnie Bell showing Brandon Aiyuk he’s ready for big role

SANTA CLARA — Brandon Aiyuk knows first-hand how challenging Kyle Shanahan's system is for rookie wide receivers, which makes what he has seen from Ronnie Bell even more impressive. Not only was the rookie 49ers receiver been active in the offense during the NFL preseason, but he also was involved in the return game. "He's doing a great job," Aiyuk said multiple times Monday, just for an emphasis. "He's pushed our unit forward in a good way. Coming out here handling his business in the preseason games. Going out there practicing every day. I've seen a lot of rookie receivers come in here and not be able to, myself included, and not be able to handle whether it's the grind of a whole entire training camp or the mental aspect it. "He's done a great job with everything, so I'm excited to see where he can take it to." Bell was involved in the 49ers' offense in the first two preseason games but not as much in the third. The snaps reduction likely was because Shanahan and the coaching staff had seen enough of what the seventh-round draft pick was capable of, penciling him onto the 53-man roster. Bell caught 10 of his 15 targets for 172 yards in San Francisco's first two preseason...