The Legislature is expected to debate an assault-weapons ban and other gun-control measures in the first session since last year's Aurora theater shootings, but Second Amendment activists want lawmakers to reject those measures.
The rally comes a day before the governor's annual State of the State address.
Democratic Gov. John Hickenlooper has said he wants lawmakers to debate gun control, but he hasn't elaborated on details.
Some Democrats want to see an assault-weapons ban and more frequent mental health alerts on gun background checks.
Some Republicans have said they'll seek legislation to increase armed security at schools.
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