First of all, if it's an Axis, there's no getting the bolt handle up in a hurry!
What kind of work have you done to the trigger, sear, or bolt assembly? Off the top of my head, I would guess the lip at the top of the cocking ramp may have been ground down or the firing pin spring has been altered to be lighter.
I'm mostly familiar with slam fires, which are frequently caused by too little sear engagement and manifest themselves when rapidly closing the bolt.
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