Not much change in only 20 years. Especially considering we still use a machinegun created 80 years ago, and that a pistol created almost 100 years ago is still considered one of the best.
But as improvements come, they will be huge advances in the scopes. Scopes will have integrated range finders that adjust the reticle automatically for the range of whatever is in the cross hairs. They will have external or eventually integrated environmental sensors which feed the data directly into the scope which adjusts the cross hairs accordingly.
There will be small improvements in the accuracy of the rifles themselves due to mechanical engineering and improved materials alone (nothing electronic or computer aided in the rifle itself). Rifles will become lighter and either retain the performance of current heavier rifles, or show improved performance.
Granted, even after such scopes and newer rifle designs come out, it will be much, much longer before they are universally adapted by the military. This being due to expense and logistical issues and a cost/benefit analyses. These rifles and scopes will be top of the line, but not military issued.
As technology advances beyond that, you will start to see improvements to the rounds themselves, to the point where the nose of the bullet is servo controlled and can adjust itsef in flight. A computer in the scope will feed target data to the microchip in the bullet. Once fired, the bullet will since outside forces acting on it–such as an unexpected gust of wind or tiny uncalcualable variable–and adjust the bullets flight path accordingly. We just started fielding some troops with the Integrated Air-Burst Weapon which shows the Army’s willingness to spend a shit load of money on computer controlled rounds will imbeded microchips. So this isn’t as far fetched as it once was. Plus I believe guided bullets have at least reached the experimental stage? Not sure. But in the next 20 to 50 years? Absolutely. They’ll exist, at least as working prototypes.
So basically the next major improvements to rifles will be the scopes. The next major step after that will be self-adjusting bullets. At no point will we ever see a man-portable servo controlled, remotely fired sniper rifle fielded for military use in a sniper roll. They may easily show up on little robot sentries like on the DMZ, remotely controlled guard towers (though an M2 hooked up to an RWS would serve just as good a purpose and already exists, so why bother reinventing something with a different rifle??) or something else stationary. But not something deployed by a sniper in the field.
A sniper in the field will see servos controlling his bullets before he ever sees servos controlling his rifle.
Again, as these super scifi desings become reality, they will still be very slow to become part of the military inventory. And that even depends on what conflicts the future holds. The more war, the more quickly we see advances in military equipment. The less war, the more these scifi weapons stay in the prototype or concept phase.
Caseless or electronic ignition bullets will be the last thing to come, if ever! Even the servo controlled bullets will be fired through conventional methods of primer and firing pin. I think that by the time such a thing would be practical, we would have completely redesigned the propulsion system in the round from powder to something else entirely.
