The difference between point of aim and point of impact at varying ranges when mechanical offset is not taken into account.
other guns?” she said while clutching my off - duty carry pistol. I’d just purchased a custom $155 holster for my gun! T ey need to cover that topic at some annual wives’ convention: How to ascertain which carry gun is their husbands’ favorite and the proper tactic to acquire it for their own personal use. Within eight hours, I’d replaced my pis- tol with an almost identical model. I showed my beautiful bride her new carry piece and the 21st-century high-tech laser that I had purchased for her. She asked me how to re- move and where I was going to store it. “You said people who can shoot don’t need those things, right?” I did say that. T e $200.00 laser unit was taken off and cast into the box of broken-hearted and unused toys. As I put it away, my wife re-appeared like a fun-hating ninja and barked, “But don’t sell it...we might need it later.” I sullenly closed the window on my laptop and dis- continued my listing on the online “for sale” website. T at high-tech piece of equipment languished in my parts box, consorting with the other holsters, lights and sights that also never got their turn to dance at the party. T en one day we planned an isolated camping trip to a river on private property. I knew everyone would want to shoot a little, so I threw it in the bag just for kicks. What I neglected to bring was enough .40 caliber ammunition. As the daylight faded, more and more friends wanted to try the laser-equipped M&Pc. It was quite the hit. At optimal range, it was like cheating and
no one seemed capable of a miss. However, when moving out to a distance of 25 or 50 yards or attempting a target as close as 3 yards, the mechanical off set issue with a laser became clear.
The AR Model I was reminded of our department’s yearly patrol rifl e qualifi cation that requires head- shots at the closer ranges. It’s always easy to tell who has been practicing mechanical off set and who hasn’t when scoring the tar- gets. Some would argue that a high level of precision isn’t necessary in a defensive sce- nario, but the facts argue otherwise. Good guys miss more than they hit in gunfi ghts and every inch counts.
We put a lot of work into developing solid marksmanship skills in the hopes of hit- ting where we aim. Proper sight alignment, grip and trigger control should be enough to make that happen, but unfortunately, it’s not. One must also train for that devil mechanical off set. By defi nition, it’s the dis- tance between the sights and the bore axis and has an eff ect on the diff erence between point of aim (POA) and point of impact (POI). A more knowledgeable and purist gun writer would discuss the true defi nition of “point-blank range,” but frankly, I think the battle over that term was lost long ago. Instead, we’ll skip it and think of mechani- cal off set as a kind of “Kentucky Windage” for defensive arms. T e shooter needs to understand his/
her equipment and any outside forces that may aff ect the bullet’s fi nal resting place at a particular distance. Simply put, the greater the distance between the bore and the sight plane, the more compensation that must be made to hit at various distances. A common argument among AR-15-style rifl e afi cio- nados is whether one should choose a 25-, 50- or 100-yard (or meter) zero. No mat- ter what zero distance is chosen, the shooter must compensate for the rifl e’s mechanical off set at close range. Since the typical AR has about 2.6 inches of mechanical off set, the shooter must remember to aim between 1 inch and 2.6 inches high at distances of 15 yards and closer respectively. At 15 yards, the shooter must aim about an inch and a half high in order to put the round in its desired spot. At 10 yards, that distance increases to about 2 inches. Finally, at three yards, one must compensate about 2.5 inches for their rifl e’s mechanical off set in order to make that precise shot. T ese numbers change slightly between diff erent rifl es and shooters, but they’re very close in my experience. T is phenomenon is not exclusive to AR-15-style rifl es. Mechanical off set can also be an issue with defensive pistols.
Lasers
With most duty pistols, the mechanical off - set between standard sights and bore axis is negligible and has little eff ect on the dif- ference between the (POA) and the (POI) until the shooter moves back to quite some distance. However, the phenomenon will become an issue with most pistol-mounted laser sighting systems. Back in the days when “going viral” was a bad thing, laser sights weren’t really accepted among professionals in the fi rearms instruction business. T ey were widely considered fragile and did not hold their zero well under recoil. T at state- ment doesn’t ring quite as true anymore. Many laser sights in current production are sturdy and well suited for a defensive fi rearm. T ey come in a variety of makes, models and variations. One can have a laser mounted in place of the guide rod, on the trigger guard, on the rail (in combination with a light, if so desired) or as a back strap replacement on some models. Crimson Trace has even teamed up with manufac- turers like Smith &Wesson and Ruger so consumers may purchase a laser-equipped gun directly from their favorite “fun shop,”
33 The Police Marksman Jan-Feb 2014
www.policemarksman.com
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