Re: 4000 fps in a 7mm STW w/140 Bullet?
one more time! You often can gain a hundred to a hundred fifty feet per second over many of the reloading manuals (Sierra, Hornaday right off the top). But your looking at 600 fps over the Hornaday manual, and at least 500fps over the older Hogdon manual. That's like trying to kiss and make up with your ex in court!
The 7STW is well into overbore, and just about anybody that shoots it a lot will confirm this. This means that you've entered into the relm of deminishing returns for what you add into the equation. Look at three magnum rounds with 139/140 grain bullets, and the .280 Remington:
a. The .280 will push a 139 grain bullet to about 3,000fps with a heavy charge of 55 grains of 4831.
b. the 7mm Rem. mag takes 63.5 grains to get to 3100fps, and 73 grains of Magpro to get another 100 fps. Ackley stated in his book that he felt the 7mm mag was about it for powder capacity with the 7mm bullet diameter, and works best with the heavier bullets. (he liked this round by the way)
c. The 7mm WBY mag is another to look at. It's got a slight larger case volume than the Remington, plus some other features that help it better with the bigger bullets. It takes almost two more grains of 4831 to get to 3100fps (first clue about overbore), and takes almost 71 grains of 4831 to get to 3400fps (I have to question the velocity that hornaday posted here)
d. now we move upto the big fellas! The 7STW needs a little over 71 grains of 4831 to get to 3300fps, and this should tell us right away that the case is in serious over bore. But 83 grains of H1000 will get you to 3400fps (Hornaday manual). Hogdons lists two loads with the 140 grain bullet that are almost 3500fps. One used IMR 7828 and the other was with H1000 (82 grains???) Compaired to the .280, we are seeing almost a 40% increase in the powder charge to gain 400fps! (4831)
e. (I know I said three) Then we come accross the 7mm Ultramag! Case looks like metal Montecristo cigar tubes! Takes 96 grains of H1000 to get to 3500fps! No wonder they have a short barrel life span! Hogdons must love this round! Yet the Winchester 7WSM with 76.3 grains of Magpro will do 3300fps! I seriously doubt this round with 115 grains of powder could do 3700 fps, let alone crack the 4000fps mark with the smaller 7STW