* Gun makers' shares rise after Las Vegas mass shooting
* U.S. factory activity surges to a more than 13-year high in Sept
* Indexes up: Dow 0.7 pct, S&P 0.4 pct, Nasdaq 0.3 pct (Updates to close)
By Caroline Valetkevitch
NEW YORK, Oct 2 (Reuters) - U.S. stocks started the fourth quarter on a strong note on Monday, with all three major indexes hitting record high closes as data pointed to underlying strength in the economy.
A measure of U.S. manufacturing activity surged to a near 13-1/2-year high in September. Disruptions to the supply chains caused by Hurricanes Harvey and Irma resulted in factories taking longer to deliver goods and boosted raw material prices.
Among the sectors with the biggest gains on Monday were materials, industrials and financials.
Optimism about tax reform also continued to bolster stocks. President Donald Trump last week proposed the biggest tax overhaul in three decades, but offered scant details.
The small-cap Russell 2000 posted another record high close. Small-cap companies are expected to be among the biggest beneficiaries of a tax cut.
"There are a lot of details (on tax reform) that need to be worked out, but the market is certainly willing to believe that something good might happen," said Scott Wren, senior global equity strategist at Wells Fargo Investment Institute in St. Louis.
Economic data has also helped, he said. "The services number is a better indicator of what's driving the economy, but it's nice to see the manufacturing number pick up."
The Dow Jones Industrial Average rose 152.51 points, or 0.68 percent, to 22,557.6, the S&P 500 gained 9.76 points, or 0.39 percent, to 2,529.12 and the Nasdaq Composite added 20.76 points, or 0.32 percent, to 6,516.72.
All three posted record high closes.
Details were still emerging on the deadliest mass shooting in U.S. history. A gunman killed at least 58 people and wounded more than 500 more in Las Vegas on Sunday. Shares of gun makers rose, including Sturm Ruger, up 3.5 percent.
General Motors was up 4.4 percent and hit an intraday record high after brokerage Deutsche Bank said the carmaker could launch driverless cars on a large scale in 2020.
Advancing issues outnumbered declining ones on the NYSE by a 1.82-to-1 ratio; on Nasdaq, a 2.36-to-1 ratio favored advancers.
About 6.3 billion shares changed hands on U.S. exchanges, about even with the daily average for the past 20 trading days, according to Thomson Reuters data. (Additional reporting by Ankur Banerjee, Gayathree Ganesan and Yashaswini Swamynathan in Bengaluru; Editing by James Dalgleish and Dan Grebler)