No plow, overseeded in fall with fertilzer and ryegrass and I feed clover seed in mineral year round. I assume you fertilize your range grasses, but perhaps not.
Our summer and fall grasses are of poor quality, compared to many other parts of the country. To achieve a high weaning weight percentage without a lot of imputs is not possible. Having said that, my counterparts in the northern states are having great grass quality at that time. They shoul have no problem achieving at least 55 to 60 % weaning weight ratios if they are using the proper type of animals.
As for frame who cares, I personally want a functional 1200 lb cow, and its going to be a a F1 Brahman type animal. I personally love the use of hybrid vigor in cattle. Its one of the few freebies we get in the cattle biz