Originally Posted by Jcub
But the .280 Ack IS the '06 case, with 4 more grains of powder. So you're saying that those 4 extra grains are the difference between Retumbo working or not?
It only takes SLIGHT differences in rifle calibers all using the same parent case to make a substantial difference. Here's a parallel: take your water hose and put the older spin on cap on it and tighten it down making the hole smaller. What happens? The same water spits out faster and flatter.
Take your question in the opposite direction. Compare the 30.06 and the 338-06. By your questioning, shouldn't H1000, and Retumbo work optimally in it? The answer is no, in fact, the powder burn rates get faster again.