going to start reloadin the 7mm08 and planning on loading 100 grain sierras and 139 grain sst hornady. how do i go about pickinv a powder that will work for both bullets?

One way is to ask someone to run QuickLOAD on it and tell you what the results are. I have done this.

The two best choices I see in the results are Re15 and H4895. There are other powders listed that yield higher velocities but not by much. Of these two, I think H4895 is the best choice based on the kinds o0f results I have gotten using it in other cartridges.

Varget is another option and a good advantage to it is how temperature stable it is.

Varget is my go to powder and has been since it came out for the 7mm-08 but I only load 140's for it. IMR 4350 was my choice before the introduction of Varget. I agree though with RR Quickloads does show those he chose as good choices.

I'm running Varget also, behind 140 gr Nosler Accubonds in my 7mm08. Shoots very well.

All of the Hodgdon powders suggested above are part of their "Extreme" line which is supposed to give consistent pressures in the temperature extremes we experience here in Texas. If you've ever worked up a hot load in December that cratered a primer in July, you'll know how big a deal this is. I've had great luck with them. I'd suggest getting a pound of Varget and another and testing them in your specific rifle for accuracy.

Varget or H4350 gets my vote.

Also, when picking a powder for a certain caliber with a certain bullet, I want the powder to be in the 90 to 100% case fill, and be in the proper burn rate for max velocity with the bullet I am wanting to use. In this case, the 7-08 will give a near case fill with Varget and the 100 grain, and will have near a 100% fill with H4350, maybe slightly compressed. There are always certain powders that go together like peas and carrots for certain calibers and bulet weights. H4350 is hard to beat, since it shoots so well with all the necked down 308 cases (7-08, 260, 243, etc).

I havent reloaded for the 708 but have researched it and agree with Varget and H4350.

I will get one at some point and I sure like the idea of running the 120 TTSX at 3k out of a lightweight 20" gun

My 7mm08 performs well with 140GK's, and shoots great with 100gr Sierra HP's using IMR 4895.

Load anything else? If so look at Varget closely. I load everything from 223 to 300 win mag. with varget. That includes 30-06, 308, 6.5, 7x64, 223, 300 win. and 6.8. The only thing I load differently is 243. Haven't found a load for it.

dont load anything else yet. got some varget so well see how it works

As said above, Varget is a good one. RL15 is another, plus N-540.

A great dual bullet combo are 120 grain Nosler Ballistic Tips & 120 grain Barnes TSX/TTSX. In my 7-08 they shoot to same point of impact, which is important to me.

I use Varget mostly because it has performed well in my .308 my 7mm-08 and my 6mm and i cant afford to go try 5 different powders im sure there are better ones but Varget has worked well for me

I haven't loaded a 7-08, but load several 308's and other weapons
larger and smaller..Both of my 308's (same case)shoot touching hole groups w/loads about .05 grains off max with Varget..and so
do any number of other weapons. I've loaded w/most everything you can get for most weapons but prefer Varget most of all powders I now load..I wore out a couple of Mag. Rifles in 300 and
7MM w/IMR 4350, but rarely got as good of results overall in any
of them as I do w/Varget..I do load RL 15 and RL 22 in a couple of rifles with good results..25-06 ect..DD

I currently load for 2 7mm-08 rifles, a Ruger 77 and a Remington M7. The Ruger prefers 120 gr Nosler BalTips and 120 gr Barnes TTSX. The Remington really likes the 130 gr Speer BTSP. Both rifles get their best velocity with Re-15, followed by IMR4320, then Varget. Accuracy is top-notch with all 3 powders.