First off, let me say you really know how to poke a stick into a sleeping dog with your 338 comment. I am sure no one would have said anything anyway but you likely lost a few useful replies the way you started your post.
No flame intended at all, just an opinion.
As far as shooting the 100 and 120 gr in a 1-9 twist. If the rifle is built well with a good barrel, a 1-9 twist barrel will shoot the lighter bullets just as well as a slower twist barrel. The only time I have ever seen an industry standard twist barrel not be accurate with light bullets was when velocity was so high that the bullets structural design would not handle the stresses of being launched at high velocity.
With the chambering your using, velocity will certainly not be a problem to cause any structural problems with any 100 or 120 gr bullet in 7mm.
I would honestly be a bit more concerned about the other end of the velocity range. Being in Montana, I generally give my barrels an extra inch of twist rate just because there is a real chance they may be used in extreme cold conditions and in these situations a marginally stabilized bullet will have severe accuracy problems from time to time.
Personally, I probably would have opted for a 1-8.5 twist so you would be covered in every situation with the small 7mm. Realize that the WSSSM will not even match the 280 Rem in most situation so a 180 gr Berger is a pretty big bullet for that class of chambering. Not that it will not work well but in many cases, if you drop bullet weight a bit, say to a 168 gr VLD, you give up a bit of BC but you also gain a significant amount of velocity potential so in the end, ballistically, the lighter, good BC bullet will outperform the slower, higher BC bullet out to a certain range.
Anyway, you should not have any problem at all with your rifle and any conventional bullet weight in 7mm.
