December 29, 2008
Petzal: The Problem With Guesswork
By David E. Petzal and Phil Bourjaily
I’ve written before that the only ballistic information you can believe is what comes out of your barrel and hits your targets. This was driven home yet again last week when I ran some drop tests on my beloved 6.5x55 New Ultra Light Arms rifle. I use two loads in it: the first is Norma factory rounds firing 156-grain Oryx bullets at 2,508 fps; the second is a handload that shoots the sensuous, attractive 130-grain Swift Scirocco at 2,750. I sight in the Oryx loads (of which I am fond because they don’t punch dinner-plate-sized holes through 90-pound deer) to hit 1.5 inches high at 100 yards; this is fine for 90 percent of the shots you get at whitetails. The Swifts print 3 inches high, and if I think I may get a long shot I use those.
However, until last week I was relying on guesswork to figure how much the two slugs actually dropped, so I went to the range and found out. The Scirocco was no surprise; it dropped 7 inches below the point of aim at 300 yards. The surprise was the Oryx. I first tried it at 200 yards, and it dropped only 2 inches below the point of aim which is odd because it has a low ballistic coeficcient, not much velocity, and is zeroed pretty low.
“What ho,” thinks I, “maybe I can use this sumbitch at 300 yards,” so I tried it, and it fell off the paper. Going by the holes in the backstop, the Oryxes dropped 17 inches from the point of aim, which means it is a dandy 200-yard bullet, but no farther.
So now I know, rather than assume, and there is a world of difference between the two.