In the USMC we use whatever we can get our hands on, which usually isn't an Elcan. Many M249's I've seen have ACOGs (or as we know them: RCOs) on them and even a few M240 B and G variants with them as well. Haven't fired a 240 with an ACOG but I have fired a 249 and I can say that it's a nice addition. I've also seen EOTECH models on some 249s.