The Senate on Monday passed a bill to extend a ban on guns that can't be detected by x-ray machines and metal detectors.

President Obama signed the 10-year extension of the Undetectable Firearms Act into law before midnight, using an auto pen as he traveled to Africa for ceremonies honoring the late South African President Nelson Mandela. The device Mr. Obama used to sign the bill has been used for the signatures of traveling presidents since the administration of George W. Bush.



The law, first passed in 1988, was set to expire on Tuesday, at a time when plastic guns created by



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Even after the mass shooting in Newtown, Conn., in December 2012, other efforts at gun control this year have been stymied by conservative opposition. However, the renewal of the Undetectable Firearms Act has had bipartisan support. Retiring Rep. Howard Coble, R-N.C., sponsored the bill in the House, and it has the support of the National Shooting Sports Foundation.

The influential National Rifle Association did not take a position on the bill, but it did say it would fight any attempts to broaden the law, including a proposal from Sen. Chuck Schumer, D-N.Y., to require plastic guns to include permanent metal parts to make them more detectable.

Mr. Obama is currently traveling to South Africa for a memorial service honoring Nelson Mandela, but he has signed a few bills by autopen when away from the White House, including the fiscal cliff bill.