With their fourth-round pick, the Bengals selected North Dakota State's Cordell Volson to help bolster their offensive line depth. The plan was not to have Volson starting on the o-line unless injuries piled up but Volson ended up beating Jackson Carman for the starting left guard gig.
While Volson ended up starting at left guard for the entire season, there was certainly room for improvement. He was okay as a starter and considering that wasn't supposed to be his role shows that he was better than expected. Volson was a fourth-round pick who ended up finding a starting job on the offensive line and that's worthy of a high grade.
Seventh-round picks are going to be looked at differently than guys taken in the first three rounds because any decent production you can get from them is a win. Jeff Gunter appeared in 10 games for the Bengals during his rookie season and he played in 29% of special teams snaps with just 6% of defensive snaps under his belt.
The Bengals got more out of Gunter than a lot of teams get out of their seventh-round picks but by the end of the season, he was held out of games as a healthy scratch. If he were a Day 2 pick, he'd receive a much worse grade but for a seventh-rounder, I'll give him an average grade.