sorting in a matrix

Hello,

I'm using a matrix report in SSRS and I'm trying to control the Sorting in a column grouping.  I have fields 'AUM', 'BUYS', 'NEW_MONEY', and 'SELLS' in the grouping.  It will only let me sort it A to Z or Z to A.

Can anyone help me with sorting with a expression?  I would like the order to be 'BUYS', 'SELLS', 'NEW_MONEY', then 'AUM'

Any information would be greatly appreciated.

Thanks,

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