but do the x models have any phsyical differences to the production models?
What Lifer said.
Yes there are sometimes changes. Usually they are very minor. Maybe a different toolbox door, a change in the routing of wiring, moving a switch or gauge etc. Rarely they major as that would have caused a model number change
A few pieces of equipment are made in such low quantities that they never get past the "XM" stage. Many "XM" items are upgraded later and loose there identity as an "XM".
Other kinds of equipment gets the "XM" designation, too. Not long before I retired (2005) I was teaching an advanced marksmanship course at the Marksmanship Training Unit and one of the arms room rifles caught my eye due to most of the black finish being worn off the lower receiver. It was an M16A4 that had stared life as a XM16, been changed to an M16A1, later to an M16A2 and then to an M16A4.
About a half of the side of the receiver was covered with stamped and over-stamped markings from all the changes. It had been in the inventory for over 40 years and still measured and gauged withing spec so it was still soldiering on as a training unit rifle. I often wondered haw many soldiers that rifle served with.
Lance
