Excellent! Gas port/gas block alignment was one of my guesses so I can be a little more confident in the future. I did throw a lot of them out there though so one was bound to stick. 
Now that you probably have a better idea if you will keep that barrel and/or receiver you can carefully file the M4 ramps into the barrel extension. I would use a lot of magic marker to make marks where the receiver ramps are and go very slowly, a little at a time, to make sure you don't remove more than necessary. Don't do it without removing the barrel or you run the risk of filing some of the finish off of the receiver (not that it is a big deal).
Now that you probably have a better idea if you will keep that barrel and/or receiver you can carefully file the M4 ramps into the barrel extension. I would use a lot of magic marker to make marks where the receiver ramps are and go very slowly, a little at a time, to make sure you don't remove more than necessary. Don't do it without removing the barrel or you run the risk of filing some of the finish off of the receiver (not that it is a big deal).
