There are lasers which do not use visible wavelengths (infrared laser diodes--1.06 micron wavenlength light). Can't be seen without special optical equipment similar to night vision light amplifiers.
http://www.springerlink.com/content/n655124412x9616u/
In regards to some earlier posts about the smaller caliber, could have been the .204 Ruger. I may be biased because the animals I have taken down for game are quite large, fast and deadly I am a firm believer in velocity, mass and specific designed bullet types.
My most reliable big game stopper thats not a shoulder killer is the .338 Winchester, the intermediate long range thats out to 400 yards is the .308 Winchester with 150gr. Barnes Triple Shocks. Thats the round I keep available for my Springfield M1A, it feeds well, shoots well and is a good medium sporting and self defense rifle cartridge.
While I have several rifles chambered for the 5.56/.223 that cartridge to me is relegated as the “pray and spray” use, or when you have the odds against you, returning covering fire or a bullet you can haul around all day in a certain mass amount.
Almost any caliber or bullet can be a sniper round, its the shooter thats a sniper.