Doublez,
Your post was reason enough for me to go back and review my loading/shooting notes on the limited experience i had with 8133. My extremely small sample of data appears to support your notion about 8133 gradually building pressure. And as it turns out, it was not that far behind Retumbo in velocity. It appears that I can get similar velocity to Retumbo by using 2 more grains of 8133. In other words in 70 grs Retumbo gets me 2900 FPS, 72 grs of 8133 gets me there too. All i did was a powder ladder with it in my 7mm RM with the 180 ELD looking for the top end. I think I ran out of room in the case for more powder before I hit pressure. If my gun had a longer throat it may be ideal. I am now thinking i need to revisit it, shoot some groups, and see what I come up with. Thanks for the input