The actual rule reads
Sporter Class 10.5 lb weight, larger then a .230 cal
Light Varmint Class 10.5 lb weight any cal
Heavy Varmint Class 13.5 lb any cal
There is no sense going into more depth here.
If you can only have 1 gun a 6PPC, 6BR, etc, fits all 3 classes. A .224 cal fits LV and HV. Now I am going to say something and I know this will bring all of the experts out who will disagree, but I really don't care. "ALL THINGS BEING EQUAL"! 14 lbs will outshoot 13 lbs, 13 lbs will outshoot 12 lbs, 12 lbs will outshoot 11 lbs, and on and on. A 13.5 lb rifle is easier to handle then a 10.5 and will, because it is easier, outshoot a 10.5 lb. Are you at a disavantage? YES but not that much. The accuracy of both is equal. So, 1 gun get a LV, if you can afford 2 guns, 1 LV and 1 HV but go out of your way to get the same in both classes, ie same style of action and action configuation, same stock, same scope, and most important the same measurements.