When you take a new or unknown rifle, a new or unknown scope, and throw in some new unknown loads the reason for lack-luster results is a bit of a guessing game. That's not even brushing on an unknown shooter and the closely related unknown bench technique.
It's nice to know something, instead of guess something or hope something.
For instance; if a rifle shoots something else very well, its a good bet the gun isn't broken.If it hasn't proven out on something already, there is always the chance that it won't shoot anything.
If the scope just got pulled off your favorite, best shooting target rifle its logical to conclude that whatever the problem is it isn't that. Without that confirmation there isn't any real reason to trust it. Broken scopes are common.
Without a way of verifying the rifle and or scope, its a little hard to automatically assume the problem is the loads.
By the sheerest of coincidences I recently worked up a 165 Ballistic Tip/Varget load for my little Anschutz 1574. Results were initially pathetic, but at least I had a history with the rifle that would suggest that it probably shouldn't shoot anything that bad. Since I had a load of known accuracy to fall back on, I was able try that long enough to prove that it would no longer shoot those either. That lead naturally to viewing the Zeiss scope with suspicion. Sure enough, it had picked that inoportune time to pile up. Swapping to a proven VX3 proved it. For what little its worth the load ended up being 46 grains of Varget loaded to fit the mag (max load from the Nosler manual)