First, you need to determine if the problem is indeed bolt stick. When the gun stops firing, is the bolt staying forward? Can it be reset manually? If it is bolt stick, then you need to use the next larger carrier.
Originally Posted by Frontal
Another possibility is a leak in the on-off top. It could be an intermittent leak which is why it is hard to notice. A leak here would prevent the bolt from resetting properly. It is possible that CO2 could exaggerate a flaw in the teflon on-off top o-ring while firing.
Another possibility is a bad regulator seat o-ring. It could be making the regulator pin stick and preventing the gas from flowing into the front part of the valve.