600U was very popular in his time. As stated, homo black and polled and a pretty good phenotype compared to other black simmental bulls at the time. He saw heavy use. His most popular sons were Nichols Blk Destiny D12 and LRS Preferred Stock 370C. I don't recall his progeny as being "big" at that time. I thought they were moderate compared to the other tall simmental bulls at the time.
The "Leachman" is Jim Leachman of Montana. He sold lots of bulls in that era including bulls from cooperator herds. Circle S was the cooperator herd that produced the bull. As I recall, the bull sold to a commercial operation. Leachman saw the bull later and bought him back to use in his simmental operation. ABS purchased an interest as well and sold lots of semen.
A few calves are still recorded each year. Less than 10 per year since 2017. The bull still has decent EPD's. A lot of the bulls from that time will have EPD's in the bottom 10% of the breed for growth and calving ease and birth weight. His API is 130 which is breed average.
600U is the great grandsire of my 17 y/o cow. I used that last straw of 600U on her granddaughter to try to get Kenny a bull calf. If successful, Kenny's bull will have 600U on both sides of the pedigree.