The full size .270 cartridges deliver high velocity with big game hunting weight bullets, and since kinetic energy is basically a function of bullet weight times velocity squared, these high velocities mean that there is plenty of downrange energy to initiate bullet expansion and inflict fatal damage on the target.
High velocity also makes for flat trajectory and an extended maximum point blank range (MPBR), which makes accurate bullet placement easier. And bullet placement is always the most important factor in killing power.
The good sectional density (SD) of the popular 130, 140, and 150 grain bullets also contributes to the cartridges' killing power. To kill quickly a bullet must penetrate deep into an animal's vitals, and sectional density is an important factor in penetration (as, of course, is adequate bullet design).
The 130 grain .270 bullet has a SD of .242. This is identical to the 100 grain .243 bullet (also noted for deep penetration) and similar to the 140 grain 7mm and 165 grain .30 caliber bullets. It is considerably superior to the 150 grain .30 caliber bullet (SD .226) to which the 130 grain .270 load is often mistakenly compared.
The 140 grain .270 bullet has a SD of .261. This is similar to the 120 grain .25 caliber, 129 grain 6.5mm, and 170 grain .30 caliber bullets.
The 150 grain .270 bullet has a SD of .279. This is similar to other bullets famous for deep penetration such as the 160 grain 7mm bullet, the 180 grain .30 caliber bullet, and the 250 grain .35 caliber bullet.
The long 160 grain bullet has a SD of .298. This is comparable to the heavy 175 grain 7mm bullet, 200 grain .30 bullet, or 220 grain 8mm bullet. According to the Nosler Reloading Guide this bullet can be driven to over 2800 fps in the standard .270 Winchester or 3100 fps in the .270 Weatherby Magnum. Zowie!
Perhaps these figures and comparisons, when coupled with the high velocity and excellent down range energy delivered by all of the .270 cartridges, begin to explain their excellent killing power.