2can, there are several ways to go about it but you don't need to load several rounds of a single powder charge to "check it". Figure a starting load, in this case let's say 38grs of varget, load three rounds and put them and a small piece of paper with the data on it in a baggie. Then load 3 rounds with say 38.5 and put them in a baggie along with the data. Repeat until you get to let's say 40grs. If you're starting out with a clean barrel, load up a couple of extra of the 38gr loads to use as foulers that don't count.
Shoot each loading group at a different target. I usually put several of the 1" stickers on a sheet of notebook paper. When I'm finished shooting, I transcribe the load data onto the targets and put the sheet in the loading log I keep for each rifle. Now then, as I shoot, I take a good look at each case after I have shot it. (I wait 1 minute between shots so I have time) Then I put it back in the baggie and shoot another. When I shoot loads 39.5 and 40, I pay particular attention to the case: how do the primers look? how did the case extract compared to the lighter loads? is there any extractor engravings in the head of the case? Is there any change in the clarity of the engravings on the head?
If not, I load another sequence of three rounds. Maybe dropping the lower charge weight and fudging past your old max. Up to say 41grs or, depending on how your cases looked at 40grs, up to 41.5. Somewhere along the way, you should get a loading that is just a little tighter than the others. That is what you're looking for. Let's say it's 40 even. I would load another sequence of 5 rounds each of 39.5, 39.8, 40, 40.3, 40.5. Once I've determined the best loading for that powder, I'd play around a bit with the bullet jump and probably call it happy. If you're below the book max, so much the better. The animals you kill with that loading will never miss the 100 or 200fps that you are MAYBE losing.
Of course, you may find that your rifle will tell you that it can't abide Varget. Or Vmax bullets. And then it's back to the drawing board. That's why most reloaders have a whole bunch of 1/2 cans of powder (or some of the nicest rose bushes in the neighborhood) I usually try at least two different brands of bullets when I start out.