Without getting too specific, large-capacity gun magazines are not legal in Colorado. There are a few variances to this law, but generally speaking, if a magazine can hold more than 15 rounds of ammunition, it is illegal. This law was enacted in 2013 in response to the mass shooting at an Aurora movie theater that left 12 people dead and 58 others injured. The shooter in that incident used a high-capacity magazine during his attack.
Since then, many gun rights advocates have argued that the ban on high-capacity magazines does nothing to prevent shootings from happening and only serves to make it more difficult for law-abiding citizens to defend themselves. There is some evidence to support this claim – since the law went into effect, there has not been a significant decrease in the number of mass shootings in Colorado.
If you have any further questions about gun laws in Colorado, we recommend contacting a local attorney or the Colorado Bureau of Investigation.