UPDATE: Firing outside managers, as Vanguard has done three times for its Explorer mutual fund since December, doesn't always boost returns.

For example: In December, Vanguard dropped Tri-State Bank's Chartwell Investment Partners, of Berwyn, from Vanguard's Explorer and Mid-Cap Growth funds. How'd that go?

ClearBridge, founded in 1962, targets stocks that are potential "category leaders" that invest for "long-term, sustainable growth," Vanguard said in its statement.  According to SEC data complied by Nasdaq, ClearBridge at Dec. 31 invested $97 billion in nearly 1,200 companies, especially tech, healthcare and consumer  stocks, led by UnitedHealth Group, Comcast Corp. (Philadelphia), Biogen, Anadarko Petroleum, Microsoft, TE Connectivity (Berwyn) and J&J, among others.

For the firms Vanguard is dropping, the loss represents significant assets. At Dec. 31, Kalmar had $2 billion invested in 127 socks, particularly consumer cyclicals and healthcare, led by West Pharmaceutical, Acxiom, Wageworks and Cooper Cos. Granahan had $3 billion in 254 stocks, with more than half in tech or healthcare, led by Abiomet, Brooks Automation and LendingTree.

Explorer advisers will now include Wellington Management (around $4 billion), Vanguard Quantitative Energy Group (more than $2 billion), and ClearBridge, Arrowpoint Asset Management, and Stephens Investment group, which split the rest (plus a small cash position). Vanguard doesn't expect the move to change Explorer expense ratios.

Vanguard CEO Bill McNabb said in his statement that the company's Portfolio Review Department will "scour the globe" for better "active" stock-pickers.

Though it's well-known as a purveyor of funds indexed to the S&P 500 and other market benchmarks, Vanguard traces its origins to its actively-managed Wellington stock-and-bond fund, started in 1929, and to active manager Wellington Management Co., which remains a Vanguard fund advisor, with offices in Boston and Philadelphia.