I would think 165gr. is too heavy, but you just never know for sure until you try them.
Yes, sizing to .316" or possibly .3165"/.317 would be better yet. Much depends on the crown and how easily they start.
Of course, pure lead will likely need to be used. At most, perhaps 40:1 would be OK. The bullet must oburate to fill the grooves.
With only 3 1/2 thou of rifling depth, the 40:1 might work well, but I'd start with pure lead.
The shorter the bullet, the easier starting and seating.
I found for a commercial lube, Lyman's Black Powder Gold works well on REAL bullets in pistol and rifle, so would do well
with your bullet too.
The 4 (squarish) grease grooves of this bullet should hold enough lube for the job at hand. Another lube that will work is SPG.
If you want to make your own lube, 60:40, BX and Vaseline is as good as ANY commercial lube I have used.
That has been my experience, in muzzleloaders shooting slugs as well as BP Ctg., guns.
I hope some of this is usable.
Working with a new gun/barrel, I find quite exciting.(in my old age - lol)
Lubing first, then sizing is the best scenario. Then, no damage to the bullet is done. I have sized lubed bullets down .009", from
.375" to .366" without any damage whatsoever. If done in a lube-sizer, the bullet will collapse if not lubed first. You won't know what
diameter a pure lead bullet will come out at, from a .319" mould. It might need no sizing at all, but I expect it will come out at .317:" to .318"
depending on the actual diameter of the mould.