Colorado House Democrats passed new ammunition limits and expanded background checks as part of a package of bills responding to recent mass shootings.
The debate on the measures has attracted attention from the White House.
The Democratic-led House voted Monday to ban large-capacity magazines, placing a limit of 15 rounds for firearms, and eight for shotguns. Lawmakers also passed a requirement for background checks on firearm sales between private parties.
Republicans oppose the measures, saying they restrict Second Amendment rights and won't prevent mass shootings.
Vice President Joe Biden called four Democrats Friday during a daylong debate on the measures, including two in moderate districts.
Lawmakers also passed bills to ban concealed firearms on colleges, and require gun purchasers to pay for their own background checks.
The Senate still needs to consider the proposals.