I'm confused here but that's not rare.
Using Hodgdon data.
The 30-06 shooting a 200gr jacketed bullet over 53.7gr H4350 will achieve 2580 fps @48,400 CUP.
They only supply data for up to 220gr bullets.
The 338-06 shooting a 200gr jacketed bullet over 62.0gr H4350 will achieve 2729 fps @54,300 PSI.
They supply data for up to 250gr bullets.
They use the same case for goodness sake so why can we push the 338" bullet so much faster? Why can't we use the same charge in the 30-06? I'm sure it has something to do with the wider bullet but I know very little about why. I'm also at a loss as to why they supply data for bullets 30gr heavier than those in the 30-06. The 338-06 will push a 250gr bullet as fast as a 30-06 will push a 200gr bullet with the same powder. Again, it's the same darn case!!!
Can anyone clear this up for me?
As several people have touched on, the first issue is what pressure you want to run at. People say pressures in CUP can't be converted to PSI, but that's not really true. It can be converted, there's just a huge amount of noise in CUP measurements. If you take them again on another copper crusher, the value you get can vary by several KCUP. So the real answer is we don't know very much about the pressure of the first load. So we're working with some ancient data in the .30-06 that probably isn't very accurate.
Second, bore diameter matters. If you remember your physics, acceleration = force/mass, and in this case force is pressure * base area. So the larger base bullet of the same weight will accelerate faster. This has two counter-acting effects. The bullet accelerates faster, but because it goes faster the pressure falls off faster since the reaction vessel is enlarged as the bullet moves down the bore. These relationships are tricky math-wise, and are the reason we have Quick Load to do the math for us. But in general the bigger the bore is and/or the lighter the bullet is, the faster a powder we'd want. So the optimum powder for the .338-06 will be faster than for the .30-06.
If we run in QL with a target pressure of a very safe 55 KPSI (65 KPSI would be safe in modern guns chambered in high pressure cartridges, but that's an argument for another day) we see that H4350 in the .30-06 gives us 54.0g charge and 2574 ft/s out of a 24" barrel. So it's very close to the Hodgdon data, and I think we can replace that 48,400 CUP mystery number with 55 KPSI and call it good. The case is 99.4% full.
QL in the .338-06 (55KPSI target) gives 6.18gr and 2722 ft/s. So again it matches the data very closely (QL really is incredible). The loading ratio this time is 109.2%, so some compression. In terms of getting velocity, H4350 is a much better fit - it's too fast for the .30-06, but better for the .338-06. The .30-06 is really going to want something like IMR 7828 SSC (if you don't care about temp stability too much) or RL-16 or H4831SC if you do. You could pick up almost 100 ft/s at the exact same pressure just by switching to RL-16.
If it's my .30-06 shooting 200 grainers, and I knew it was 100% good to go and chambered in higher pressure rounds like the 270 with no mechanical changes, I'd probably target pressures in the 62KPSI range and use RL-16 and expect to get about 2740 ft/s at max charge and hopefully over 2700 ft/s with an accuracy load depending on where the top node was.
