Archive | February, 2013

Dissipator style AR-15 carbines are experiencing somewhat of a resurgence in popularity lately. Manufacturers like Spike’s Tactical, Palmetto State Armory, ADCO Firearms, and others have made it easier than ever to buy one. Even Bravo Company Manufacturing has flirted with the idea of releasing one.

The term Dissipator as it pertains to AR-15 carbines refers to a specific upper receiver configuration with a false front sight base in the same position as it would be on a rifle length gas system and a carbine length (or more recently, mid-length) gas system with low-profile gas block located under rifle length hand guards. This configuration was originally created by Bushmaster Firearms International LLC to offer rifle length sight radius along with the handling characteristics of a carbine and it was mostly successful at doing so.

In the era that it was conceived, an era without reliable red dot sights, this was a valuable combination of characteristics but does it hold value today? Honestly, I’m still not sure but I think the answer is…maybe, for two reasons.

Advantages

One of the oft touted advantages of Dissipators is based on a contingency. Dissipator uppers are more reliable than a 20″ barrel with a rifle length gas system that has been cut back to 16″ (these types of barrels can be made to function fairly reliably, but the gas port must be opened significantly to make up for a severe lack of dwell time). So, while it is true that a Dissipator is more reliable than a cut back rifle barrel, it isn’t necessary to cut back a 20″ barrel in order to get a 16″ barrel. With the widespread availability of 16″ barrels with reliable carbine and mid-length gas systems, this isn’t really as much of an advantage as it used to be.

The advantages that come with having a longer hand guard are more concrete and a Dissipator upper is one of the simplest and least expensive ways to get a long hand guard on a 16″ barrel, especially if you aren’t going to use free-float hand guards. Longer hand guards have a couple of advantages. They allow for a wider variety of support hand placements, the increased surface area can make it easier to mount items like your sling and weapon light without interfering with your support hand placement, they allow you to move your light closer to the muzzle to reduce shadowing caused by the barrel, and I find a longer hand guard gives more options when supporting the rifle on a barricade or support surface like a shooting bag. Certainly, there are other ways to achieve a longer hand guard on a short barrel, but none are as inexpensive or easy as a Dissipator style upper.

The original reason for the creation of the Dissipator is still one of its advantages. It does offer increased sight radius over most other 16″ barrel configurations. This is especially handy if you are going to use the iron sights instead of an optic. In recent years, with the advent of reliable and affordable optics, this has become less of an advantage.

One Big Disadvantage

Dissipators have one big disadvantage: weight. The weight from longer hand guards and 2 gas blocks (1 false, 1 low profile) adds up quickly and represents a significant difference. That weight is on the barrel, which is probably the worst place to add weight from a handling perspective.

A 16″ mid-length upper with a lightweight barrel profile weighs about 2 pounds 2 ounces without hand guards, BCG, or charging handle. My Dissipator upper which also has a lightweight barrel profile weighs 2 pounds 8 ounces without hand guards, BCG, or charging handle. Keep in mind that the Spike’s GMP is probably the lightest Dissipator style upper available, so the gap may be wider with other uppers. The difference in weight increases once the Dissipator’s longer hand guards are in place.

I am sure that some of you are saying that the weight difference isn’t all that much. However, the real question isn’t whether or not a Dissipator is too heavy. It is whether or not the perceived advantages that Dissipators offer merit the extra weight, especially with the availability of reasonably priced and extremely reliable red dot optics that offer superior performance to iron sights. Is a Dissipator worth the extra weight if you are just going to relegate your iron sights to back up status? That is what you will have to decide.

Why Choose a Dissipator?

I said above that I think the answer is maybe for two reasons and here they are. First, a Dissipator makes sense first and foremost if you are going to eschew optics all together and use only iron sights. This mitigates the weight issue and the increased sight radius really does help, especially as engagement distances increase. Second, if you are on an extremely tight budget, Dissipators do offer a lot of hand guard for less money. The upper receiver itself or the complete rifle will cost a bit more but not really as much as buying and installing an extended hand guard on another carbine.

That is it. If you don’t fit into one of those two camps, then just admit that you want one because they look cool (which is perfectly valid).

A Word on the Spike’s Tactical GMP

I have had experience with several Dissipators over the years – everything from original Bushmasters to home built models that use clamp on front sights. None of those compare to the Spike’s Tactical GMP (an AIM Surplus Exclusive). The GMP really represents the way a modern Dissipator should be configured.

First and foremost, the GMP features a lightweight profile barrel which makes it significantly lighter than other Dissipators that I have used. Second, and perhaps just as important, it utilizes a mid-length gas system that is reliable, soft shooting, and overall a better fit for the characteristic of a 16″ barrel. Additionally, both the low profile gas block and false front sight base are actually pinned to the barrel which is an extremely nice touch. The false front sight base has a stainless steel pin that protrudes from where the gas tube would have been to lock the hand guard cap in place in absence of the gas tube. Mine has been very reliable so far and very accurate.

My GMP upper currently wears rifle length Magpul MOE Hand Guards with an IWC QD Micro Flush Sling Mount installed and an attached Surefire G2X in a IWC SMC Light Mount and a Troy Industries Fixed Rear BattleSight (great choice due to lightweight and same-plane aperture). I have spent time with both a Magpul MVG and an IWC Weapon Control MOUNT-N-SLOT installed on the hand guards and both work well.

Wrap Up

There are two reasons to consider a Dissipator given the current availability of other options. If you are going to use only your iron sights or you can’t afford to buy or build an upper with an extended free float hand guard, then a Dissipator may be a viable option for you. Otherwise, given the availability of inexpensive, high quality optics and low profile gas blocks under extended hand guards, they are not necessary or even optimal.