From a guy who's dealing with one, don't get the echo 1 m28, and along those likes are the other two m24 versions. I can't remember. It I think the Javelin is the same as the echo 1, dunno about the uk arms.
I've heard the utg getting some good upgrades and being a formidable gun. But truthfully for what your doing, the best idea would be the g700.
And that field sounds very small... Not much sniping to be done..
Edit: my suggestion, get an AEG and try that out first, then go out to some real fields and see how sniping works and what you can do to become one