Anyone know what twist was used on the old 1950s era FN mauser Weatherbys? (in .300)

I have a listing that shows that the new 300 Wby twist is 1-9 1/2" but that the old was 1-12". The problem: don't know just how old is old.
Of interest is the Vanguard has a 10" twist, the same as Winchester, Sako, and Remington.
I know that Roy was all about velocity so maybe he used the slower twist right at first. You'll probably need to measure.

Thanks,my crude measurements, using a tight brush and cleaning rod, are coming up between 10-12, with a bit of assumption on exactly where the rifling starts.

At any rate 200g NP aren't shooting as good as lighter bullets, not keyholing, but disappointing accuracy. I'll keep trying knowing I may have to live with lighter bullets.

In the 1969-70 Weatherby catalogue they were still using the 1-12 twist in the 300. I picked this catalogue up at an auction for a buck and it is pretty cool. When you read through it and look at what was available at the time, and then realize Roy had been at it for 20 years already at that time, He (Roy) was decades ahead of anyone. It is really interesting to note the difference in foreign relations at the time.