The folks at L3 have been busy in the skunk works department coming up with a tool that precision shooters will appreciate. The device sitting on top of the Barrett is the L3 Integrated Optical Systems. There are proprietary components of this technology, so you’ll need to excuse the absence of an in depth discussion.
The L3 IOS is built on the U.S. Optics SN3 variable powered day optic. It integrates an electronics package that ranges, and develops a firing solution taking into account the weapon system and caliber, environmental conditions such as temperature, relative humidity and barometric pressure (without a handheld weather meter); along with other capabilities. Compensating for wind is left to the operator. The ballistics computer generates a G1 and G7 firing solution.
Older ballistic computers have relied on the G1 calculation, which is based on flat based projectiles, so the calculated elevation for a given range and set of conditions was never precise when using modern ammunition. The discrepancy results from the sniper using a bullet geometry that is different from the assumed geometry in the G1 calculation. L3, has included the G7 calculation which is based on modern bullet geometries and closer to the ammunition in use today, hence the ballistic calculation is more precise with the improved ballistic coefficients of modern ammunition.