[reynolds357]

Originally Posted by jmr40

Both momentum and energy are irrelevant and no one has paid any attention to either in years.

Momentum is a good way to predict how well a bullet will knock over a steel plate, but does nothing to predict how well bullets perform inside living creatures when the bullet hits.

Energy numbers alone are useless. They CAN be used to predict how well a bullet will expand if all other variables are removed from the equation, but that isn't possible. If you're comparing very similar bullets then energy numbers might be somewhat useful. If not you can easily get very misleading information. This is especially true when comparing different calibers.

Here is what you need ask when choosing bullets.

Does the bullet give adequate penetration to reach the vital organs of the game being shot?

That is based on the bullets sectional density and construction. The Interlock bullets you used are sorta middle of the road as to construction. Others are tougher and will penetrate deeper, others are softer, will expand rapidly and may not penetrate enough to reach vital organs.

What is the bullets sectional density (SD)?

That is a ratio of the bullets weight and diameter. Within the same diameter a heavier bullet has a higher sectional density and assuming equal construction will penetrate deeper. The 180 interlock will out penetrate the 150 interlock by a good bit. But if you were shooting a soft 180 gr bullet and a tougher 150 the tougher 150 will penetrate deeper. On deer size game any of them will give more than enough but on bigger game the deeper penetrating bullet might be needed.

But when you change calibers it gets interesting. A 30 caliber/180 gr bullet has about the same SD as a 26 caliber/140 gr, a 27 caliber/150 gr a 28 caliber/160 gr and a 33 caliber/225 gr. If we are shooting the same type bullet in all of those calibers penetration in game will be virtually the same.

Will the bullet impact at the speeds it was designed to work?

The interlocks you chose are typical of most bullets and work well if they impact between about 1800 up to about 2800 fps. If they impact below about 1800 fps they don't expand and act like FMJ. Above 2800 fps and they may over expand and not penetrate. But not all bullets are the same. Some will stay together well over 3000 fps, but those are also the bullets that need more than 1800 fps or they don't expand at all. Some need to impact at 2000-2200 fps to work. You don't choose the same bullet for a 308 and 300WM.

The 150 leaving the muzzle at 3000 fps are very likely to fail at close range. Once they slow down at 100-150 yards would work better. Or just use them in a 308 where they are starting at about 2800 fps. If you're going to shoot 150's at 3000 fps you need to choose a tougher bullet designed to work at that speed.

It's just too complicated to try to use simple energy or momentum numbers to predict which bullets will be more effective with modern bullets. Back in the 1700's with smokeless powder and round balls those numbers were relevant. Not anymore.

I am a huge fan of kinetic energy. Shoot critter of choice with a 7-08 140 grain then shoot another one with a 7RUM 140 gr.