@Silver ... I agree that just any old cow won't raise the 700 lb calves. Genetics has a WHOLE LOT to do with it.
That said, you seem to have some pretty darn nice cattle and good genetics.
Here in Va we get a different kind of grass from year to year. This year we had pretty decent rain.. but it varied in a 50 mile radius. I had dairy farms with real good corn crops and some that had stressed corn all within 50-75 miles. The amount of rain had a big effect on the grass too. We had some good grass at a couple places and 20 miles away the grass was also washy... you could see a definite difference in the calves. And also, we don't sort our cows to put "better cows" together and not so good cows other places. We more often sort by bull (steer) calves and heifer calves to make getting them in and a trailer load of all the same sex to go to certain places. So there will be some good cows and some mediocre cows all together at the same place. Granted the good cows will do better but on places where we have had way more rain than normal and the grass is washy, even their calves will not be as good and the mediocre cows calves sometimes actually do better because the cows are making more milk sometimes. But overall, the condition of the grass does dictate A LOT of the calf weight through the effect it has on the cows too.
Because we do some buying and selling of breds, sometimes doing what
@Dave does and buy some one and dones if they can be bought right, we have varying degrees of "good cows" and mediocre cows. The nice ones often stay and become a part of the herd; or their heifer calves will join the replacements. I've kept a few heifers off one and dones because those cows were old for a reason, and the calves showed the quality even if the old cow was just at the end of her productive life.
With the way the markets have been here, my son is doing more dabbling in buying cheap bull, and even some cheaper steer calves, working them, getting them bunk broke, weaned and in better shape... and then putting together some groups. He did a few last year, have about 40 now and as soon as there is a little more money will try to buy a few more to get preconditioned for sale. Unfortunately, we spent a kings ransom on putting in the bunker for corn silage this year because concrete has gone through the roof... he hates dealing with the bags and the mud in the winter and bag prices went way up; this was something he had been wanting to do but would not do it until the farm was his obviously.... and this after he just made the first yearly payment on the farm that he bought from the deceased friend's widow that we have been renting.... So, just when the conditions seem right for some cattle "dealing" we are also dealing with alot of output that we didn't have 2 years ago. But, I am hoping that we can do a little more this year.... We cut some of the cow numbers back to about 130-150 and put some of these calves out on grass after 30 days in the barn lots and they are looking real good. We had a good grass year and now it is doing them alot of good.
Gotta work with the system that we have... and the market demands that is in this area.
Love your red cows and we get massacred on reds here....