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I ran powder tables in QuickLOAD based on the 270 grain Speer Gold Dot and a 250 grain Sierra Tournament Master and also tried a 240 grain Speer soft point and a 300 grain Sierra soft point. These were seated to max overall length and with a variety of case water capacities (bigger is better here, so get the lightest weight commercial cases you can). The 250 and 270 were the better performers.
The table results showed 296/H110 was the top powder every time (Hodgdon tech told me these are the same powder from the same plant shipped in differently labeled drums). From an 18" barrel the 250 and 270 grain bullets produced 1670-1833 fps in maximum pressure loads depending on case capacity and whose maximum pressure standard I employed (C.I.P. or S.A.M.M.I., 40,600 and 36,000 P.S.I., respectively). In any event, one of these powder designations is what you want to use. Pick whichever costs less at the moment.
The 300 grain bullet requires a 24" barrel and the higher C.I.P. maximum pressure in a large case to just barely make it to 1600 FPS. That is a bit close for comfort. The advantage from attempting it is the high sectional density of that bullet will retain both more momentum and energy out to 300 yards than the other two. However, if you go down to an 18" tube, the only way to get that speed is with the greater powder capacity allowed by the 250and 270 grain bullets.
The 250 grain match bullet retained more energy (5%) and had 75" of drop verses 86" for the 270 grain bullet at 300 yards from an 18" tube. The 270 won on retained momentum only, being 11% greater than the 250 at that distance. This might not look good for the 270, but that thin skinned target bullet (the only 250 grain .429 in my database) probably performs better than other shapes will. A 240 grain soft point just didn't keep up energy or momentum out to distance, owing to geometry.
For shorter ranges this question of energy matters a bit more. The shorter the bullet, the lighter it is and it has less ability to retain momentum over a distance, but it does allow more powder capacity when it is seated. The energy at the muzzle comes from the powder burned behind it, and in this case the 296/H110 burn fast enough to have good ballistic efficiency even in a carbine, so the light bullets will get you more energy up close. The difference declines with distance.
The bottom line is, you will have to choose a barrel length and a maximum distance to define what bullet is best.
Nick
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