All,

Between operational/reliability considerations -

What is the difference between the M&P15TII series and both the lower priced Sport and XV series?

Obviously there is a difference in form-factor/furniture/features, but I am curious on the aspects that affect reliability.

For example - it appears the barrels are the same 4140 steel. From the outside looking at that spec it would appear to me the lifespan of the barrels would be equal - you would loose performance at equal rates over the long term. If there are differences in the specific 4140 mix that make a difference I don't see then that would be something to know.

What about recoil, trigger pull, and overall reliability - IE - more stout butt stock vs lighter butt stock (more/less durable), more/less robust firing mechanism, easier/harder to jam, smoother/rougher trigger mechanism, etc, etc?