Veterans usually swap helmets and cleats for hats and sneakers in the preseason finale. In other words, they're the players on the 75-man roster who don't play.

Rookies, on the other hand, are the ones soaking up valuable on-field experience prior to their first ever 16-game run in the National Football League.

For the San Francisco 49ers pair of first-round draft picks, the latter experience is likely to happen this Thursday night against the San Diego Chargers.

Both DeForest Buckner and Joshua Garnett sounded excited on Monday when discussing their final regular-season tuneup. Each rookie has moved up from the third team to joining the starters on their respective side of the ball.

With Arik Armstead sidelined this preseason with an upper-body injury, Buckner has made two starts on the defensive line. The seventh overall pick out of Oregon sat out of the Week 2 road victory against the Denver Broncos with a minor injury, but he's still produced four tackles in two exhibition appearances.

"It's been great to get my feet wet and get to know the speed of the game," said Buckner, who was on the field for 25 snaps in last week's loss to the Green Bay Packers.

Garnett, the 28th overall pick out of Stanford, has been pushing veteran Zane Beadles for playing time as San Francisco's starting left guard.

Garnett explained that he's intent on using the San Diego matchup to continue his case for the first-team job.

"This is the finale before the season starts," Garnett said. "It's a time to really put everything together, come off the ball, play low and really leave it all out on the field."

Garnett has been one of the most active 49ers in the preseason. The rookie guard has played 97 snaps in three games for an offense that leads the NFL with 184.7 rushing yards per game this preseason. He most recently worked with the first-team offensive line, playing 30 snaps against the Packers, beginning on San Francisco's third possession of the game.

Garnett's depth-chart climb is even more impressive considering the 6-foot-5, 321-pound lineman had to miss the team's offseason program due to Stanford's graduation date.

"I know I get frustrated sometimes, but I have to remember I missed 20-something practices in the spring time," Garnett said. "I'm still trying to play catch up. Every day, I'm trying to close the gap. When I'm out there, I don't think people are saying, 'Well, he missed so many practices.' I think I'm blending in well. It doesn't really seem like I've missed too much time, but I've still got a lot of work to do."

Garnett's first-team snaps also added to his confidence. Facing well-known defenders can certainly do that.

"It was exciting to get out there with Joe (Staley) and (Daniel) Kilgore and be able to go against Clay Matthews, Julius Peppers and (Mike) Daniels – guys who are elite players in the NFL," Garnett said. "To be able to know that you're able to work on techniques and know that's as realistic as it's going to get, it really felt game-like. I feel like those were great experiences for me."

Buckner, on the other hand, said he didn't focus on the individual players he's facing in the preseason.

"I think about the next opponent," the defensive lineman said. "When we're watching film, I'm trying to gain every advantage I can. When I'm on the field, it doesn't matter who is in front of me, I'm trying to play my game.

"I believe in my abilities and try to play with a lot of confidence so I'm able to make plays."

Thursday night's preseason finale will be another opportunity for each player to build on the improvements they've made.

"As a young guy, you're hopefully going to get a lot of playing time," Garnett said. "We know we have a little bit of a break before we play the (Los Angeles) Rams, so it's time to really go all out in this last preseason game."