Alliant Techsystems Inc. (ATK) has agreed to buy sports optics company Bushnell Group Holdings Inc. for $985 million in cash from private-equity firm MidOcean Partners, a move that will broaden the defense-focused company's capabilities in commercial shooting sports and expand its portfolio of branded shooting sports products.

The deal will also allow ATK to enter new sporting markets in golf, snow skiing and camping and comes as defense suppliers like ATK face an anticipated federal spending curtailment.

Bushnell makes branded sports optics, outdoor accessories and performance eyewear. The company sells products like binoculars, riflescopes, trail cameras, laser rangefinders and GPS devices. It was acquired by MidOcean in August 2007 in a deal that was reported to be worth $500 million to $600 million and made a number of acquisitions in the past six years.

The deal is expected to close in the December or March quarters.

Bushnell's sales for 2013 are expected to be about $600 million. ATK expects the acquisition to hurt per-share earnings for the year ending in March. However, the company said it expects the deal to add to per-share earnings in fiscal 2015, the first full year of operations. It also estimates that fiscal 2016 per-share earnings will be bolstered by $1.

"The Bushnell acquisition is consistent with ATK's focus on establishing leadership positions in our core markets," ATK Chief Executive Mark DeYoung said in prepared remarks.

ATK will integrate Bushnell into its sporting group within its existing accessories business.

ATK, which makes conventional munitions and rocket motors, in May agreed to buy hunting rifles and shotgun company Caliber Co. for $315 million in cash, a move that added long guns to its brands in commercial and security ammunition, shooting sports and security-related accessories.

Shares of ATK closed Wednesday at $97.21 and were inactive premarket. The stock has risen 27% in the past three months.

Write to Saabira Chaudhuri at saabira.chaudhuri@wsj.com

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