I'm reloading some 165 grain nosler partition spitzers, for my 300 Weatherby, my question is for a 1:10 twist on the barrel is the 165 grain o.k. or do I need to go with a heavier bullet? Or what is the minimum weight bullet for a 1:10 twist barrel?

165's should shoot fine,my 300 Weatherby loves 168 gr TSX's

Ya, I'm hoping that I make it out to the range soon to try them out.

I have a friend who shoots a .30-.378 with 165 gr. TTSX bullets. I believe the twist in that rifle is l-10" and these bullets work fine, actually better than fine.

I never had any problems with 165's in my .300 Wby. However, mine was a Sako with a 1:11 twist rate.

If a 180 will work, why wouldn't a (presumably) shorter 165 work? Or do I have it backwards?

I had a 30-378 that loved the barnes 150 xlc. Took a 6x6 elk a few years back quartering away at a whopping 80 yards. Bullet enter by rear of rib and exited the off shoulder. The bullet was still going so fast and was evidently still pretty intact as it turned that off shoulder bone to mush. Elk never took another step.
I love the guys that say you can't use lighter bullets in magnum rifles... apparently they don't own a calculator. HMMMM lets see.....a 180 grain that loses 40% of it's weight on impact or a 165 that keeps 95% of it's weight......which is better....decisions decisions.

Dayton:If the 165's won't shoot well in your Weatherby, the 10" twist won't be the reason. I've shot thousands in 10 twist 300 mags,H&H,Winchester and Weatherby, and they have shown fine accuracy out to 500 yards.

If some individual 300 Weatherby shot better with 180's, maybe due to the 180 handling the long Weatherby free bore,I could understand that as well. But a 10 twist works fine with 165's.