That's what I thought as well, but it seems so over the top that I can't believe that's what it means. Especially when there are some called the same thing, but 310 and stuff like that as well.
I did think it might mean fps, 'cos I saw 310 first, but that seems low for a sniper, then I saw 260 and now I'm thinking it can't possibly be fps.
seen a few comments from googling vsr springs that is percentage from original or something like that. 260=260% increase over original spring. Dunno if this theory is right though. I've never really researched too much into snipers.