SIGHTING IN ON: Laser Sight Mechanical Offset

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SIGHTING IN ON: Laser Sight Mechanical Offset
By Warren Wilson

“So, that’s the only one you have,” I questioned? “And that’s the bottom price?” Her response was a silent nod and solid eye contact. That is the manager Michelle’s way of making me understand that she’s serious at my local gun shop, which she runs. Smith & Wesson M&P40c pistols with the Crimson Trace laser grip were in high demand in my area and I was desperate, so I haggled no more and just made the purchase.

I really didn’t need the laser, but I needed the pistol…now. You see, after finally convincing my wife to switch from a revolver to an auto pistol for concealed carry, she almost immediately latched onto the pistol I carried off-duty. Standing alongside my wife in front of my open gun safe was nearly my downfall. “Can’t you just carry one of these other guns?” she said while clutching my off-duty carry pistol. I’d just purchased a custom $155 holster for my gun! They 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 pistol 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 remove and where I was going to store it. “You said people who can shoot don’t need those things, right?” I did say that. The $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 discontinued my listing on the online “for sale” website. That 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.

Then 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 offset issue with a laser became clear.

The AR Model

I was reminded of our department’s yearly patrol rifle qualification that requires headshots at the closer ranges. It’s always easy to tell who has been practicing mechanical offset and who hasn’t when scoring the targets. Some would argue that a high level of precision isn’t necessary in a defensive scenario, but the facts argue otherwise. Good guys miss more than they hit in gunfights and every inch counts.

We put a lot of work into developing solid marksmanship skills in the hopes of hitting 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 offset. By definition, it’s the distance between the sights and the bore axis and has an effect on the difference between point of aim (POA) and point of impact (POI). A more knowledgeable and purist gun writer would discuss the true definition 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 mechanical offset as a kind of “Kentucky Windage” for defensive arms.

The shooter needs to understand his/her equipment and any outside forces that may affect the bullet’s final 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 rifle aficionados is whether one should choose a 25-, 50- or 100-yard  (or meter) zero. No matter what zero distance is chosen, the shooter must compensate for the rifle’s mechanical offset at close range. Since the typical AR has about 2.6 inches of mechanical offset, 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 rifle’s mechanical offset in order to make that precise shot. These numbers change slightly between different rifles and shooters, but they’re very close in my experience. This phenomenon is not exclusive to AR-15-style rifles. Mechanical offset can also be an issue with defensive pistols.

 

Lasers

With most duty pistols, the mechanical offset between standard sights and bore axis is negligible and has little effect on the difference 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 firearms instruction business. They were widely considered fragile and did not hold their zero well under recoil. That statement doesn’t ring quite as true anymore.

Many laser sights in current production are sturdy and well suited for a defensive firearm. They 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 manufacturers like Smith &Wesson and Ruger so consumers may purchase a laser-equipped gun directly from their favorite “fun shop,” without the need to purchase the laser sight unit separately.

Tradeoffs

The guide rod models seem to be more prone to breakage for obvious reasons of heat and the stress put on them inherently by their position in the firearm, but they have the least mechanical offset at about one-half inch.

The trigger guard models are easy to mount, but prohibit the use of standard holsters and their offset is about 2 inches. They are prone to losing their zero after sustained firing.
The same can be said for rail-mounted units and they tend to get clogged with powder from the muzzle blast and require frequent cleaning to maintain their projection ability. The mechanical offset of these units can be from 1.5 inches to 2.5 inches, depending on whether they are only a laser model or a light/laser combination.

Finally, the back strap replacement models that are made for the Generation 4 Glock (or back strap additions for the Generation 3) and the Smith and Wesson M&P models do allow for the use of the holsters already available. The actual laser is mounted a good distance from the muzzle and they also appear to be the most durable of all the different variations. The replacement grip panel laser for a 1911-style pistol also falls into this category.

As with most good things, there is a tradeoff. These models have the most complicated mechanical offset issues. The Crimson Trace used in this test is not only offset under the bore axis but also to its right. That means that the shooter may have to compensate for two different directions while firing outside of the optimal range.

 

The Test

According to the paperwork, this Crimson Trace model, which came from the factory with a Smith & Wesson M&P 40c, is zeroed at 50 feet. However, we found ours much more comfortable at 21 feet (7 yards) with our chosen test rounds, Federal 155-grain HST. The POI/POA was almost spot-on at that distance no matter who was shooting it. Since 7 yards seemed to be the sweet spot, we tried 3 yards and 15 yards to compare the POA/POI difference.

At 3 yards, the bullets consistently struck about 1.75 inches off at the 11 o’clock position. At 15 yards, the bullets struck at the 5 o’clock position about 2 inches from point of aim. I wanted to test at 25 yards, but that is nearly impossible in normal daylight. In dry-fire, backyard testing, I would estimate a bullet impact of about 4 inches from POA at the 5 o’clock position at that distance.

Coming into this test, I would never have believed that the Crimson Trace would have performed so well. I really expected to see much more disparity between the POA/POI anywhere outside of the optimal range for the laser sight. I decided to perform an impromptu test for the average shooter. Crimson Trace seems to market their products, at least mostly, toward regular folks.

The closest thing to that in my shooting party was my wife. She was a reserve sheriff’s deputy almost two decades ago, but has received only a little training since then. I asked her to participate. The test would be to start from the low ready position and fire five rounds inside the qualification ring at 7 yards as quickly as possible. One relay would be with the laser-assisted grip and one without. She first tested the pistol with the Crimson Trace grip. Her overall time was 3.72 seconds with an average split time of 0.740 seconds. The five-shot group was a whisper over 5 inches. Sans laser, but with some more practice, her time increased to 4.66 seconds and a split time of 0.932 seconds. The five-shot group was about 9 inches and not as well centered. There can be little doubt that these little gizmos can improve a shooter’s ability to hit the intended target with increased speed and accuracy.

Lasers and other tech gear have infiltrated our world and will continue to do so. Their quality has also become better with time. I once thought that lasers were mostly for people who couldn’t shoot well. My thoughts have changed on that topic. As reputable companies like Crimson Trace continue to put out quality products like the one tested here, laser sighting systems will continue to become more relevant in the market of self-defense.

Where my opinion hasn’t changed is that officers who could potentially be using firearms for serious social work. They need to know how their equipment will perform under varying circumstances, including the potential distance of their encounter. That is the basis of adding a laser-aiming device to your pistol. The mantra is, and always should be, to Test Your Equipment. If you choose to bring a laser into your defensive battery, know where it will hit at various distances and practice.  PM

Warren Wilson is a Lieutenant with the Enid Police Department in Oklahoma.  He is a former SWAT team member/leader and has been in law enforcement for 17 years

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