Back in the spring I bought a used weatherby vanguard in .257 wby mag. Finally got a chance to shoot it with some reloads the other day, but didn't get to enjoy shooting it very much. Worked up a ladder test of 5 different load from 66gr to 70gr of powder. H1000 and 120gr nosler partitions loaded to factory length cartridge base to ogive. This was the result, the bottom left hole is 3 shots at 66gr, no need to go any further for a hunting round. Shot 2 at 69gr out of curiosity to check for pressure signs and see if it would group with a slightly hotter load, which it did not. This was at 75 yards instead of 100 as that's what our range is on our mountain ground

Nice work! Only a couple things make you feel better than finding a load your gun loves.

The Weatherby Vanguards are made by Howa, essentially a Howa 1500 made for Weatherby. They are solid rifles. I have one in .30-06.

That’s what’s called a pocket group. Repeat that performance four or five times and you might just know what you got. For example, Did you fire a fowling shot before the first three? If not, I can almost guarantee you the next group will not be that size. Sorry, don’t mean to rain on anybody’s parade But it is what it is.

Sometimes after cleaning the bore it will take 4-8 fouling shots to settle the group in.
Doug Lee
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I did not fire any fouling shots. I bought the rifle used with 11 rounds through it and it had not been cleaned since the previous owner had fired those 11

That will get you closer than a spotless, clean barrel, however, simply changing the powder will change the point of impact due to the fowling being two different powders. Copper jacket, consistency, and metallurgy will also change point of impact the difference between Hornady and Sierra, for example. Doug Lee made a very valid point. The condition of the bore, Machining marks, smoothness of lands & grooves, uniformity of bore diameter, etc. we will all determine the amount of fowling that is required to reach stability. custom barrels, take these things into consideration, and that is the reason that they generally as a rule tend to place the fouling shot closer to the “group” . congratulations on your new acquisition and I hope it serves you well in the future.