In some circles, tactical gurus speak of the ill effects of using a vertical grip on your AR. As a former operator, I find this radically amusing. Defining why and why not isn't an easy task; actually, defining why not is almost impossible for me. So cutting to the chase, I love the vertical grip on a tactical rifle. For that matter, if I were to step back into the tactical 3-Gun world, I would more than likely attach a short vertical grip to that blaster as well.
The benefits quickly outrun the negatives.
Driving the Gun When trying to drive your AR from target to target, the vertical grip works well as a reference point to position your hand in precisely the same location each time. That being said, I use a nonstandard grip on the front end of my rifle, starting with the hand wrapped around the vertical grip and the thumb either over the top or along the side of the Picatinny-railed, free-floating handguard. I prefer to run the thumb down the side as it helps point the carbine more naturally; more importantly, it allows for the activation of the infrared (IR) laser tape switch attached at the 10:30- to 11-o'clock position on the carbine. This position offers more control for starting and stopping the gun effectively. This technique is similar to that used by top 3-Gun shooters, with the only change being the addition of the vertical grip as a reference point. If you had nothing else to worry about other than driving the gun from target to target, a simple hand stop would accomplish the same task with a much smaller piece of plastic or aluminum rather than an entire vertical grip. As the carny says on late-night TV, "But wait, there's more!"
Lights, Lasers & Curb Feelers Remember the days of the curb feeler on the old Cadillacs? Other than those who roll in low riders, it seems that the curb feeler has lost its appeal. As tactical shooters, we sometimes have additional accessories add to the front of our carbines. At the very least, you should have a light that can be used for room entries and searching. For almost the entire ground-pounding sector of the U.S. Army, there are also other accoutrements that come in handy during combat operations. An IR laser is a must if you want to effectively engage threats at night; thermal is an option but not widely used at the infantryman's level and would not necessitate the use of a vertical grip. The laser, on the other hand, is generally mounted forward of the receiver and attached to the handguard. Can you manipulate an IR-laser-mounted carbine without a vertical grip? Of course, but having a vertical grip allows easier manipulation and a better hold.
Firearm Retention If shooting wasn't enough, we in the tactical world must also be concerned with firearm retention, or the ability to hang on to our carbine if we find ourselves in a wrestling match. The plan isn't to roll around on the ground with another man entangled in our rifle system, but that can sometimes become reality. I like the forward vertical grip for additional leverage as we attempt to jerk the carbine from the aggressor's hands; if this is not successful, the bad guy may use the vertical grip to our disadvantage. Staying switched-on with our head on a swivel should help eliminate some of this, but always be ready to fight until you can shoot the bad guy off your carbine.
Nonstandard Shooting Positions This is where the forward vertical grip shines. The distance from the front of the receiver is not an arbitrary measurement. This distance allows for a lethal grip when driving the gun from target to target while allowing us to bend our support arm slightly, which in turn increases strength. Straight arms are not the style when you want to shoot fast. In addition to the slightly bent elbow, I like to have enough room between the front of the receiver and the vertical grip to build a very tight prone position. If the grip is too far back, I won't be able to build this position. If I am trying to get up and down quickly to shoot under a car, the vertical grip also comes into play. Using the vertical grip to hold the front of the carbine steady works like a champ. I hook the vertical grip on my forearm as I build my position; once in position, I use the vertical grip to adjust the height of the front of the gun, as well as to control recoil.
I don't care if the buttstock is touching my shoulder at this point because the grip controls recoil and the shooting arm controls elevation. Hooking the vertical grip on your forearm works well and is a great reason to add a vertical grip, but there are many other ways to make use of this extra carbine appendage. When shooting over the hood of a vehicle, we use a position I call Junkyard Prone, or JYP. This position allows you to attain a lower silhouette while being able to quickly engage. The vertical grip can be used here if you want to snake your support arm under, in front of the magazine well and over the edge of the hood, grabbing the vertical grip. When making longer shots, this version of JYP is extremely stable and helps control recoil more than some of the other JYP positions.
When shooting the stacked feet position or down a steep grade, I also use the vertical grip to hook my thumb as I grab the bottom of my boot with my fingers. This position is fast and stable if the terrain forces you to build a whacky position; this same position also works from a rooftop.