A Springfield Armory SOCOM 16. One popular and rather simple modification to the M1A family of rifles is the venting or slotting of the upper handguard. To some people it adds aesthetic value, but it also helps cool the barrel, and at the very least, shaves off a few ounces.
However it does have drawbacks. Removing material from the upper handguard supposedly makes it fragile and prone to flexing and breaking. There is also the issue of the heat from the barrel cause distortions if using a scope. (GRH)