Yes, you can set up the 'residue' belt for each gun separately. Select Residue instead of main and enter the number of rounds you want configured (in this case 50). My Main belt has one yellow tracer every five rounds at guns 1 and 8 but this changes to 1:1 red:AP in the last 50 as you can see below. Very easy to tell the difference.
I find it interesting that the guns run out at different times. This adds to the realism for me since I bet they wouldn't be perfectly timed in RL.
