How old is the battery? A weak battery could cause those issues, where it starts off fast and then slips up.
How old is the bolt spring? A weak bolt spring can have symptoms like that too.
Have you fully tuned your level 10 bolt? Bolt stick causes the bolt to take longer to reset. The valve cannot recharge until the bolt fully resets. If the mag fires again before the valve is fully charged due to a slow reset, the mag will cough.
Except for the Automag in front, its usually the man behind the equipment that counts.