i hope this is not that dumb of question but here it goes. i am loading for 7mm mag and 7mm rum and was wondering if here is any benefit in shooting lighter weight bullets? in the rum i load a 160gr and in the rem mag i load a 150(both for deer). i have some 100 and 120 gr bullets and would not use them for deer, but are they better for varmets than the 160 and 150? and if so why? if not why do thay even make them if there is no benefit?

Personally the only reason for the "magnums" in any flavor is to handle the heavier bullets for that caliber at the same or even slightly higher velocity.
That being said the light bullets are not really made for the big seven mags as much as they are available. These lighter bullets will make for a lot of destruction at high velocities if thats what you're after. Keep in mind the differences in case capacity of what you're loading compared to the 7mm-08, 7x57, ect.

Patrick, They make 115 grain HP and 120 grain VMaxs and yes they have a purpose......7mmBR is a little different than a 7mmMag! Or the 7mm-08 or the 7x57.....Some people have only one gun and shoot varmints in the spring and summer and deer in the fall and winter. So they want a "varmint bullet" and a "deer bullet" for the same gun. Now you want to see a mess? The 115 grain Speer HP from a 7mmMag will make a "mess" of a groundhog! However the 120 grain VMAX from a 7mmBR XP-100 pistol as a "devastating" bullet up side the head of a deer!!!(note: Never use this bullet "up side the head" if wanting to mount said deer!!!) Horns tend to wilt! There is a big family of 7mm's and there is a big selection of bullets for them.....all of them have a purpose! GHD PS: In answer to the last questions about are they better and why, the 150 and 160 grain "big game" bullets won't perform(won't open up) on varmints due to the fact that they don't meet with enough resistance thereby passing on through without much relay of energy to the varmint(no shock) just making a "little hole in and a little hole out". Whereas the lighter, thin jacketed bullets tend to "shed their energy" upon impact causing big messes on varmints but also if used on big game, shed that energy to soon with no penetratin and thereby causing wounds resulting in disfigurement,slow death rather than quick humane dispatches!