I do not know about US Army Chinooks, but in the RAF we could fit mini guns to the front right and left windows and have the M240D on the ramp. If you can find some pictures of RAF Chinooks being used in the Gulf War 1991 by the Special Forces flight they may show them. The had tubes mounted by the guns to catch the spent cartridges. This combination has been used in many Operations post the Gulf one, or some sort of variation of it.
Have a look here.