600g Ribs actually weigh less than 280g

West Peak Spur, I always buy 600g pork ribs from them and I always feel their weight is very light in package compared to other Spur. I went the extra mile by weigh the package today and it weighs 306g with packaging, and 280g without packaging (with bones and all basting sauce only 280g). Do not tell me pork rib shrink more than 55% when cooked!