Arther beat me to it

Sounds to me like an arrow problem , not a broadhead problem .
Try some quality carbon , alluminum , or acc's , with 5" offset feathers and Ill bet you groups shrink cosiderably . Proper spine is critacal , allitel stiff is fine , but a littel weak will wreak havoc on your fixed broadhead , and mecanical groups . Small fletching will kill accuracy with fixed heads allso , use adaquate fletching for the job at hand .

Lenn's advise on arrow straightness , nock allignment , and insert allignment , is criticall allso , as is nock fit .

There are many pieces to the puzzel ,get one out of place and there goes your accuracy .