No, you can not discharge a firearm in Boulder County Open Space.
If you need to read it somewhere:
http://www.bouldercounty.org/play/recreation/pages/posrulesandregs.aspxQuote:
Discharging or carrying firearms, crossbows, fireworks, explosives or projectile weapons of any kind are not permitted except as expressly mandated by Article 12 of Title 18 of the Colorado Revised Statutes, as amended.
- This includes paintball, BB, pellet, air, paint ball, and blow guns; rockets, crossbows, longbows and slingshots ($300 fine).

