After a record 71 closes for the Dow so far this year, one of this year's biggest bulls is taking a more subdued view of the stock market.

PNC Asset Management's Bill Stone is telling investors not to expect such a big year in 2018.

"I've gotten a little less optimistic. It's not bad. I think we have a good chance to still clock in at some sort of high single-digit numbers," he said Thursday on CNBC's "Trading Nation."

Stone, who's the firm's global chief investment strategist, correctly predicted Washington would successfully get tax reform done before the end of 2017. He also told investors the stock market rally was intact when investor sentiment grew cautious earlier this year.

"You're likely to get a — and this may not be too much of a fearless forecast — but a significantly more amount of volatility. I do think it's going to be hard for stocks to get more expensive," he added.

But make no mistake, Stone isn't retreating into the bear camp. He doesn't see the rally coming undone or a recession in the cards. Rather, he predicts the tax reform package is a solid bullish catalyst for the markets.

"You'll probably see earnings grow somewhere around 15 percent in 2018," he said.

Yet, Stone acknowledges that the market hasn't seen a pullback this year — one that Wall Street typically deems as healthy. And, 2018 may be the year.

"The only thing I would say is maybe finally the market discounts too much good news and maybe we finally maybe peak out," Stone said.