Usually B load range is about 1100 pounds,and C is 1360,i think it depends on the tire size also.When you get up in the D load range they are usually 6 ply.
I went and looked at my Load Master C range tires..yep,1760.
Maybe its the B rating thats 1300 pound rating.I remember when i bought them there was 2 stacks of tires in the store that size.B and C rated.I had to make sure i grabbed all four the same rating.