This is no Jegan. The visor clearly makes it a GM Sniper II.

The head certainly looks like a GM Sniper II but look at the shoulders, they're completely different, and the Sniper II carries it's beam sabers on it's rear skirt armor, and the those weird elbows are also missing as well.

I never seen a GM spartan

as a matter of fact its a Gm spartan http://gundam.wikia.com/wiki/RGM-79S_GM_Spartan