AR9 lower parts kit is the same as AR15 except for the modified ejector and magazine catch. As far as the trigger goes, The AR-9 trigger has a heavier hammer than the AR15 trigger, so it hits harder.
Its design is special for the AR-9, making it hit the firing pin with more force and less shake, which ensures primer hits to make the gun go bang.
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AR Lower Parts Kit Compatibility
The AR9 lower can use most AR-15 lower parts and upgrades, like a better grip from BCM or an AR-15 trigger from a wide range of options.
AR9 lower parts kit include: