CONTRIBUTOR'S NOTE: Here's part II of my post on SOCOM's search for a precisions sniper rifle. The comments below come from an active SEAL sniper in the field now.
In the search for the best all around sniper support/modern battle rifle, I'm thinking of a gas piston system vs. a gas impingement system. This does three things: 1) keeps carbon and debris out of the chamber 2) provides the ability to adjust to accommodate suppressors and increased rate of fire 3) eliminates need for a buffer tube, allowing for folding and fixed stock options.
Which leads to my second requirement for a folding yet adjustable stock and cheek weld 1) for varieties in length of pull, amount of armor or other gear between shoulder and stock 2) length reduction, think mobility transitions, PSD, parachuting, packing in/concealment/silhouette etc.
Third point, swappable and free-floating barrels with length and twist rate configurations, 10 inch to 20+ depending on the mission (important note here: weapon to not require a specialty tool for any modifications).
Fourth, integrated rail system with enough length to accommodate back up iron sites, primary optic, magnifier and night vision optics, as well as the ability to accept the FN40GL.
Fifth, non-reciprocating side charging handle 1) eliminates need for shooter to break cheek weld to cycle weapon 2) eliminates need for forward assist button as you can seat the round in the chamber by pushing the charging handle forward 3) non-reciprocating charging handle allows for traditional shooting positions for practical and competition applications 4) charging handle capable of ambidextrous setup for left or right handed shooter, adaptable to offhand shooting positions and wounded shooter operation.
Sixth, ambidextrous buttonology (magazine release, selector switch) for the same reasons mentioned above. Seventh, this must be offered in primarily and at the very least .308 caliber/7.62 by 51mm and adaptable down to .223/5.56.
Eighth, must accept traditional magazines for both the SR-25 and M4 in the rifles converted form.
Ninth, just a reminder, no requirement of specialty tools for any modifications! See the Robinson XCR, The Magpul Masoud and Massada/Remington/Bushmaster ACR, The FN SCAR L/H, SCAR Heavy with a conversion kit for 5.56.