I have a question about compressed loads. I have never loaded any compressed loads, but I am trying some Retumbo powder in my 300 win mag with some Berger 190 and 210 VLD's. The data provided by Berger shows a max of 82.9 grains at 108% of case capacity for the 190 grain loaded to a COAL of 3.340 with a velocity of 2998fps.
This is one of the kinds of "what-if" questions that QuickLOAD is useful to study.
Modeling the Berger load in QL assuming Winchester brass, 26" barrel, and SAAMI chamber size (because I have no H2O capacity data), the resulting prediction is 109% fill (which might end up being 108% with actual water grain capacity), 3,021 fps, and 54,219 psi vs a max pressure of 62,336. From what I can see, if you can stuff it in there with out bulging the case so it won't fit in the chamber, Retumbo won't go over pressure. 109% is a lot of compression.
These bullets will be seated to a COAL of 3.558 in my rifle for the 190 grain bullet. How will the increased case capacity due to my longer COAL affect pressure and therefore velocity? Logically it would seem that the velocity may be a bit lower, but like I said, I have never run into this situation before.
I can estimate that.
Important assumption: You have at least 0.020" clearance from the lands. If you are touching the lands all bets are off and pressure will be close to 7,200 psi higher.
With that assumption in mind, the same model with just the COAL increased to 3.558" and everything else lef6t the same, QuickLOAD prdicts 103.9% fill, 2,936 fps, 48,691 psi. On that basis, the increased case volume caused by having less of it filled by bullet can be used for more powder with out going over pressure (a feature of a long throated chamber with a long bullet). Going for equal pressure to the 3.34 inch load, QuickLOAD says it would take 85.5g of Retumbo yielding 3,034 fps, but I'd work up to that. I never load to a QuickLOAD predicted max load with out backing off 10% and working up to it taking chronograph readings and inspecting brass. (some times I work up with one shot per charge in 1 grain increments looking for pressure signs and pull all the bullets after I see the first sign whatever it is (sticky bolt, polished case base, flattened primer, etc.).
I'd work up to the first load from Berger too.
The high percentage fill is an indication that the powder is marginally too slow for the bullet weight in the cartridge so I asked QL for a propellant table (load map) listing suitable powders in order of decreasing MV at the same pressure. Other powders to consider, all predicted to have higher muzzle velocity than Retumbo, listed top to bottom in order of decreasing MV:
N570
Ramshot Magnum (Big Boy)
RL25
N560
IMR7828
IMR7828SSC
Accurate MagPRO
H1000
RL22
Winchester WXR
Fitch