no reason to be on grain at that size.  they need to grow frame at this point, not fatten.  their stomachs arent really ready for grain (at 300) in their diet until closer to 500 and realistically later than that.   

There are a whole bunch of rancher/wheat farmers in oklahoma area who have the exact opposite problem as you.  wheat grass growing out their ears, wide open spaces and a shortage of calves to eat all the feed that is exceptional this year from all the rain.  Someone on market talk posted some sky high calf prices at the scott city KS salebarn last week approaching $5 per pound for flyweights i believe.  

a trip to a sale barn in wheatgrass country right now would triple your price.