AR-15 Weight and Balance (Part 1 of 3)

On the internet, the debate rages on.

What is the debate? Well, it doesn’t really matter. People will seemingly argue over anything – and I’ve been guilty of that myself.

One of the more popular debates is weight. Proponents of lightweight rifles point to carbine courses where a heavy rifle can get tiring, and accessories that boost the weight of the rifle, meaning that starting with a lightweight carbine is better. Proponents of heavy rifles say that they work out a lot, and their grandfather carried a BAR while assaulting the beach at Versailles, so weight isn’t a problem.

Another topic is balance, and this is a term that I have yet to see defined by a majority opinion. Some people like the weight to be on the front of the rifle. They load up their rail system with lights, VFGs, bipods, etc, over a heavy barrel profile, and with a standard or lightweight aftermarket stock out back. Others like a rear bias – they’ll get a Magpul UBR and stick it on a lightweight rifle with a pencil barrel and a pistol light on the handguard. Finally, some prefer a neutral balance – like myself (although I do prefer a very slight rear weight bias).

Before I dive into the meat of the issue, I’ll define something. Center of gravity (CG) – and if you’re a pilot, you’ll know what I’m talking about before I say it – is the point at which something will balance if it were suspended from that point. This is easier said than done, but with the AR-15, I’ve given it my best effort.

With an airplane, fuel is normally located at a point near the center of gravity, so that the flight characteristics of the airplane do not drastically change from the beginning to the end of the flight. Similarly, the cartridges in an AR-15 magazine are located at a point which is essentially right on the center of gravity of a stock M4 carbine. Thus, as the ammunition is expended, the balance of the rifle does not really change. What this means is that whether you’re firing the first round or the thirtieth, you won’t have to compensate as you bring the rifle up to a firing position.

With a CAR stock, CAR handguards, and the A2 flash hider, the weapon's CG is right at the point of suspension.This is my definition of a "neutral" CG for the AR-15.

This rifle weighs almost 2lbs more, but has a nearly identical center of gravity. How? Properly balancing the weight of accessories up front with a heavier stock at the rear.

You may not notice it without someone telling you to look for it, but if you have a forward weight bias – meaning that you’ve moved the center of gravity forward from the “stock” position – as you expend ammunition, the weapon will become slightly more nose heavy, because weight is being reduced at a point behind the CG, thereby shifting it forward.

Whether you have two rifles or twenty, maintaining a consistent center of gravity will help you shoot better when switching from weapon to weapon. Incidentally, when starting out on this project, I discovered that all of my AR-15s had almost exactly the same center of gravity, although weight varied as much as 4 pounds from lightest to heaviest.

Now, aircraft CG does not directly relate to weapon CG, because you’re putting different forces on a rifle while shooting it than you would on an airplane by flying it, but the basic principles remain the same. Furthermore, I won’t go into the details of aircraft weight and balance – weight, arm, moment and all that jazz – but I will explain what you need to know to fine tune the balance of your AR-15 to something that might be more agreeable to you.

First, understand that the closer the weight is to the center of gravity, the less effect it will have on the location of the CG. To demonstrate this fact, observe the following pictures.

Here, an A2 flash hider is exchanged for a Smith Vortex flash hider. The weight difference is .05lbs.

A tiny change in the attitude of the weapon. Now, watch as a magazine is inserted:

The only change made was the addition of a Magpul PMag with 28 rounds of 75gr ammunition – because the suspension point was slightly forward of the CG (note the muzzle high attitude), there was a tiny change in the attitude of the weapon. That magazine weighed 1.2lbs on a postal scale.

From this, we see that adding weight close to or on the center of gravity will have little effect on the balance of the weapon compared to adding weight farther away from the CG. Because I like to put my optics right at that natural CG, it doesn’t matter whether I have an Aimpoint or EOTech or even a 1-4 variable – the balance of the weapon will basically be unaffected.

Now, let’s see how other parts changes affect balance.

Adding a KAC M4 RAS, TangoDown SCAR rail panels, and a TangoDown stubby VFG shifted the weight forward slightly. Alone, the M4 RAS was, at .55lbs, .25lbs heavier than the CAR handguards and .15lbs heavier than MOE handguards; with TD panels and a TD VFG it weighed .85lbs.

The addition of a Vltor EMod stock shifted the weight to the rear significantly. This is because the CG of the EMod itself is way at the rear of the stock – so even though it doesn’t add much weight to the rifle in an overall sense, it does have more of an effect on CG than other stocks. In other words, if you want to balance out a front-heavy carbine without making the weapon a lot heavier, the EMod is for you. Some applications may still call for a heavier stock, though.

Swapping a rail panel (.05lbs) for a Surefire X300 (.25lbs) brings the nose down slightly…

The additional .05lbs of a Surefire G2 and polymer mount (.3lbs) bring the nose down just a little more (note: a metal head and metal “clicky” tailcap will add .05lbs each)

Finally, the .6lbs of a Surefire 9P in a Vltor offset mount bring the CG back to “neutral”, almost.

I brought another rifle and tested it (without optics) – with a VCAS sling utilizing QD swivels, the rifle was neutral…

Without the sling and the swivel at the rear of the stock, the nose of the rifle dipped a little. The forward swivel was mounted at the rear of the rail, so it had little effect on the CG. Yes, this rifle had a Daniel Defense M4 12.0 rail, Surefire G2 LED, Magpul MBUS front sight, several rail panels, and a TD stubby VFG. How did it balance almost the same as the other 16″ M4 profile rifle with an EMod in the same position? Well, the Vltor low profile gas block is much lighter than the standard FSB, the QD socket at the rear of the rifle helped, and the PWS FSC556 is a tad lighter than the Smith Vortex. Those minor changes allow me to drive the rifle with a “better” VFG position and increase the sight radius without significantly affecting the balance of the weapon.

You may be getting the impression that these changes aren’t making a very big difference. However, if I installed a RAS, VFG, light, etc and left a CAR stock at the rear, the muzzle device would practically be on the ground. Every change I made was very slight and designed to have a small effect on the overall balance of the weapon. I’d also like to note that the collapsible stocks were set at comfortable shooting positions for me – your stock usage may vary, and you should balance your rifle accordingly.

In Part 2 of this article, I will do more fine-tuning of CG relative to weight and intended usage, and in Part 3, I’ll hit the range and compare forward, neutral and rear balanced carbines.

ith a CAR stock and the A2 flash hider, the weapon’s CG is right at the point of suspension.

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4 Comments

Filed under Firearms, Tests

4 responses to “AR-15 Weight and Balance (Part 1 of 3)

  1. Mike W

    Crap, now I want to check my rifle’s CG. thanks

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  3. Pingback: POF R.D.I.K. « Vuurwapen Blog

  4. scootle

    Did part 2 and 3 ever get published? Thanks for the article. I was wondering about this exact issue with my new lightweight carbine build… and you nailed it. Great pictures.

    I’m in the aerospace biz, so maybe that’s why we worry about these sorts of things… 😉

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