Police recovered two handguns and 15 rifles at Grumberg's Saugerties residence including an AR-15 semiautomatic rifle after executing a search warrant.
The suspect also bought an AR-15 semiautomatic rifle, a military-style gun popular with sportsmen.
Unlike the military version, the AR-15 is a semiautomatic, firing one bullet per squeeze of the trigger.
The original M-16 patent ran out years ago, and now the AR-15 is manufactured by several gunmakers.
Authorities have said an AR-15 rifle was used in the Sandy Hook attack.
One officer got out of the second vehicle and fired multiple rounds from his AR-15 rifle at Dorner's vehicle.
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Despite the set-backs, it released a video this month demonstrating an AR-15 with a 3D printed part firing more than 600 rounds.
Wal-Mart, the largest munitions seller in the U.S., removed some ads to to the type of weapon (an AR-15) used at Sandy Hook.
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"An AR-15 (is) easier to shoot than a shotgun, there's less recoil in a .223 than a 12 gauge, " wrote one online user.
The rifle is a Bushmaster version of a widely made AR-15, the civilian version of the M-16 rifle used by the U.S. military.
Advocates for tighter gun laws argue there's no need for Americans to own the powerful rifle, but the gun's proponents say the AR-15's accuracy makes it safe.
Klein said gun owners are worried they won't be able to purchase semi-automatic rifles such as the AR-15 in the future, so they are buying them up now.
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The offer, capping six months of negotiations between the Department of Economic and Community Development and Freedom Group, was dropped after private equity firm Cerberus Capital Management announced it would sell Freedom Group, manufacturer of the Bushmaster AR-15.
Ysgogodd hyn Darren Millar AC ar gyfer y Ceidwadwyr yng Ngorllewin Clwyd i ddatgan fod cannoedd o eiddo yn ei etholaeth wedi cael eu hadeiladu ar orlifdiroedd oherwydd TAN 15.
Mae Cwysi hefyd yn cynnal noson yn y Foelas, Pentrefoelas, ar nos Lun, Hydref 15 am 7.30 o'r gloch, lle bydd cyfle i weld y lluniau digidol a chyfle i ffermwyr drafod ymysg ei gilydd o flaen llaw.
Seydoux has gathered 15 of the best AR.
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