Items done in paint, then rearranged and texted in photoshop.
In 2027, the US military requested a new .50 rifle to replace the now outdated M107 and M500 rifles. Snipers in the field complained that their weapons were to heavy, and were hard to reload unseen. Since the .50 rifles were provided by Barrett for 45 years, the Military instanly turned to Barrett. they came up with the M128. On the outside, it apears to be a restyled M500, on the inside, its completely different. The M500s and the M107s were gas operated. The M128 is not. It used the recoil force captured by several springs along the barrel to extract the empty case from the chamber, and chamber another round. With this change, the gas created by the explosion of the propellant charge is completely used to drive the bullet down the barrel, and does not sacrefice any power to rechamber the weapon.
Another major change is the magazine, or rather, the way of replacing magazines. It uses no conventional "inserted from the bottom" magazines. The magazines used in the M128 are insterted from the top, and are extracted that way. The reason for this change is the way the older M107 and M500 are reloaded, from the bottom. The problem with this is, that the shooter has to lift his weapon, and suspend it in midair while changing magazines. This takes a lot of effort, and it's quite visible from a distance. with the M128, the magazine just pops up from the top, and you can pull it out, place a new one, and pull the charging handle.
The final change is the bullet. The ordinary .50 BMG's lacked stopping power at ranges over 2000 meters and are not very accurate compared to the new round, the .50 BSR (Barret Sniper Rifle). the round has exactly the same dimentions as the .50 BMG, and thus can be fired from any .50 BMG weapon.
Note: its a very, very big image, sorry 'bout that
Edit: Now that i look at it for the 2nd time, i see that i forgot to type "Scope" behind "M169 4-9x40 tactical". With tactical scope i mean a scope with a laser rangefinder and autofocus.