Understanding Mechanical Offset
BY Herschel Smith4 years, 10 months ago
What’s mechanical offset and how do you deal with it? If you have an optic on a firearm, particularly a rifle, the line-of-sight through the scope is higher than the center of the bore, and that difference is what we call offset. In other words, when you take a shot the bullet is going to exit the barrel as much as several inches lower than the line of sight.
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To check this out, you’re going to need about 50 rounds of ammunition and a target. I suggest you fire three-shot groups, holding center, from 3, 7, 10, 15 and 25 yards. I think you’ll discover that your rounds are striking somewhere around 2 to 3 inches low at 3, 7 and 10 yards. At 15 yards, the group will still be low, but a little closer to point-of-aim. At 25 yards, point-of-aim and your three-shot group should be pretty close to coinciding.
Next, try shooting those same three-shot groups at 3, 7, 10 and 15 yards again, but this time hold high to account for the offset you observed the first time around (remember, the 25-yard group should be close enough to the center to not warrant significant correction). If you hold correctly, you should end up with centered hits at each of the distances. One quick example might be holding 3 inches high at 3 yards. Continue to practice getting used to the various mechanical offsets by shooting snaps—one shot standing from ready—at each of the various ranges until you thoroughly understand your offset holds.
Travis Haley refers to this as “height over bore” in the Magpul Dynamics “Art of the Tactical Carbine,” which is a very good video series. I highly recommend it.
If this matters to you in CQB, you should check out your correction on a short range.
On June 7, 2019 at 1:17 pm, Gryphon said:
If you’re using an “Optic” at under 10 Meters “Range”, you need more Backyard Range Time shooting Offhand, from the Hip, at Tennis Balls or empty plastic Water Bottles, scattered about from 10 to 30 Feet or so. It’s the main way I Practice with my Sig AR Pistol, as it is the first Go-To Weapon in the House and Yard.
On June 7, 2019 at 5:00 pm, Georgiaboy61 said:
If you want to master your firearm and its load, you must know and master its trajectory and ballistics. Ballistic calculators are a wonderful tool and aid to attaining this end, but nothing takes the place of empirical, real-world experience. You’ve got to pay your dues, no doubt about it!
On June 8, 2019 at 10:08 am, revjen45 said:
Excellent explanation of this topic.