I was able to go after pronghorn in 1991 and have taken only 9 since then, along with 10 mule deer. The .270Win with 130gr Hornady bullets has never failed to drop pronghorns or muleys on the first shot. Now, I have to admit, I am close, when I shoot, usually from 200 to 300 yds. The longest shot that I have made on pronghorns was a 325 yd shot. Hit a tad high over the heart, but he dropped without taking a step.
.270Win has been around since 1935, so the cartridge is not new or sexy, but it simply keeps on performing, year after year....AND you can buy ammo in any little country store or gas station that carries ammo.