Sounds like maybe its the regulator.Check this thread on PBN.
regulator problems - PbNation
You can attempt to rebuild the reg yourself.
YouTube - Regulator Disassembly

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Help my friend

DoW-Outlaw Squad

i actually had this problem last weekend, i aired up my mini and shot about 3 hoppers off in the back yard brought the mini back into the house went to the washroom and looked at my mini's reg and it was showing that it was at about 210-215 when i set my mini to 200 firm, i think i might just lower the reg down to 170 and see how that effects it after a little while

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