Yup.  Sounds about right.  I like to run No. 1 buck when I can find it - which is not often these days.

Just wondering if anyone has tried this intermediate buckshot pellet size.
 
In addition to the Lee 6 cavity mold offered by Track of the Wolf, this pellet size is available as a swaged high antimony pellet from Ballistic Products and as a cast "hardball" lead alloy pellet from Hunters Supply cast bullets.

These .310" buckshot pellets run approximately 44 grains or 10 pellets to the ounce. 

https://www.trackofthewolf.com/Categories/PartDetail.aspx/1202/1/LEE-310-6C

https://www.ballisticproducts.com/Super-Buck-Lead-1-1_2-8-lb_jar-310/productinfo/SBK15/

http://hunters-supply.com/buck-shot-lbs-p-1072.html

The Lee 6 cavity .310" RB mold is not a standard Lee item.  It is carried only by Track Of The Wolf.  The 6 cavity mold is an easy mold to use compared to the 18 cavity Lee buckshot mold in three traditional sizes.

Just an update for the current ammo situation. 

Nine .310" lead round balls - buckshot if you will - fit perfectly in a WAA12 wad. Indeed, in a 3 x 3 stack the pellets are flush with the top of the wad.  Depending on the lead alloy these weigh in at .91 ounce to just over .92 ounce. 

That said, look up Alliant one ounce 12 gauge load data for Winchester AA or Remington Premier STS and like Remington hulls using AA12 wads. Then substitute 9 of the .31" lead balls for shot and finish loading as normal. 

These are not long range hunting buckshot, but these are buckshot loads.

Example:

12 Gauge
2 3/4-in. Winchester AA Plastic Shells
1 shot wt.
Win 209
WAA12
Green Dot
1300 fps

https://www.alliantpowder.com/reloaders/RecipePrint.aspx?shotype=&weight=1&weightdis=1&shellid=493&gtypeid=3&gauge=12&lid=681