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AR-15 Buffer Weight (and Why It Matters)

Understanding AR-15 Buffer Weights

A wide variety of AR-15 buffer weights and springs are available —  from the cheap, mil-spec set that likely came with your rifle, to the high-end models that demand over $100.

Start to research the topic, and it’s easy to get lost in the potential benefits, drawbacks and recommendations.

Spike's Tactical ST-9X 9MM Heavy Buffer
Spike’s Tactical ST-9X 9MM Heavy Buffer

 

But the best place to start is always a basic understanding of why they matter. Then we’ll take a look at the main types of buffer weights, what they’re used for, how to use them to optimize your rifle’s gas system.

 

Is the Buffer Really Important?

The buffer may look like a paperweight, but without one your rifle is effectively an awkward, single-shot rifle.

Armaspec SRS Stealth Recoil Spring - Multiple Buffer Weights Available
Armaspec SRS Stealth Recoil Spring – Multiple Buffer Weights Available

Every semi-automatic firearm requires the use of a recoil spring and buffer weight, which return the bolt carrier group (BCG) back into battery. Without a buffer in between it, buffer spring is made to be too strong to cycle the BCG, making the buffer essential.

But the movement of the weight helps absorb the already-minor recoil of the AR-rifle.

A heavier H2 buffer takes longer to move, slows down more quickly and minimizes the ‘punch’ of the recoil while still maintaining the rifles function.

Having too much weight in the buffer can cause the rifle to short stroke, as the rifle’s gas system may not have the necessary power to cycle the heavier buffer (causing inconsistent extraction and ejection)

But having as much weight as possible increases the “dwell time” spent by the spent ammo in the upper receiver, allowing more of the excess gas and carbon to push out (cleaner operation).

More heat dissipates and there is more consistent extraction and ejection of the spent cartridge.

Getting the balance right can be affected by a fair amount of factors, including ammo types and calibers, proper installation of the gas block and tube, or the size of the gas port drilled into your barrel.

With that in mind, here’s an overview of AR-15 buffer weight sizes and how they affect your rifle.

 

Carbine Buffer Weights (3 oz)

A standard buffer is made of an aluminum housing with three puck-shaped steel weights and three rubber washers to prevent the steel pucks from slapping directly into each other.

These buffers are designed for use in traditional carbine-length gas systems and with a wide range of ammo.  They’re even more viable in mid-length systems, which place the gas block farther from the breach, lessening the amount of gas in the system and thus softening the impact of gas on the bolt.

Adjustment of this size of buffer housing, which is standard for most AR types, can be made by removing an end cap. This requires removing and replacing a roll pin.

 

Heavy (H1) Buffer (3.8 oz)

LBE Unlimited Carbine Heavy Buffers - 3 Types Available

LBE Unlimited Carbine Heavy Buffers – 3 Types Available

Heavy weights, or “H” weights, add about an ounce to the entire buffer. One of the approximately .6-oz. steel weights is removed and replaced with a tungsten weight, which is about 1.45 oz.

Adding even this amount of extra weight can cause issues on some rifles. But most AR-15s are over-gassed on purpose and can handle this type of addition.

 

H2 Buffer (4.6-4.7 oz)

The next rung on the ladder is the H2, which replaces two steel weights with a pair of tungsten weights, adding nearly two ounces to a stock buffer.

These heavy buffers can be too heavy for some carbine applications, though they are often used. An H2 is likely too heavy for many mid-length systems, but this is not where they are most often desired.

With the advent of AR-Pistols in recent years, shooters need heavy buffers to compensate. A standard carbine buffer is far too light and will likely result in violent cycling of the action.

 

H3 Buffer (5-5.4 oz.)

The H3 represents the heaviest of the carbine-length buffers for AR-pattern rifles, coming in at a hefty 5.2 oz., give or take.

Why have a buffer weighing fully two ounces over a standard buffer?

The single best advantage of the AR platform is the unbelievable versatility in calibers. In addition to the standard .223/5.56 chambering, AR-pattern rifles are found with heavier calibers such 7.62X39, .300 AAC, and some new offerings like the .204 Ruger and the .224 Valkyrie.

Above all of these are the monsters: the .458 SOCOM and the .50 Beowulf.

All of these heavy hitters are able to use a standard lower receiver assembly, but most of these systems are decidedly over-gassed. The impact of the gas charge of a .458 SOCOM with a muzzle energy of 2,700 ft. lbs. greatly exceeds that of .223 (1,200 ft. lbs).

The extra buffer weight helps compensate and dissolve that extra energy.

Pistol Caliber (5-8.5 oz.)

The heaviest buffers belong to the dedicated pistol-caliber AR platforms. These buffers often consist of a steel housing rather than aluminum and have a wide range of possible weights, often around 5 oz.

The rationale is that a direct blowback design applies more pressure directly to the BCG which slams into the buffer with no gas system to soften the blow, thus necessitating a considerably heavier buffer.

The secondary reasoning for a considerably heavier buffer for pistol caliber AR-pattern weapons is the nature of the weapons. There are a number of full-size, 16” pistol caliber carbines but an extremely popular alternative has been to go with pistol configurations.

Some manufacturers are making pistol barrels as short as 4” for AR platforms, coupled with short pistol-length buffer tubes making for a sharp blowback in the weapon.

Some of the heaviest in this category are HSS (6.5 oz.) and the XH buffer (8.5 oz).

 

Rifle-length Buffers (5 oz.)

One glance at a buffer from the A2 style fixed buttstock lets you know that it is a completely different animal.

The housing of rifle-length buffers are longer and designed to operate in the longer rifle length buffer tube —  never in any carbine or pistol systems.

If it was used, it will slam into the end of the buffer tube, possibly cracking the lower receiver.

Considering the disparity in appearance alone, this can be an easy mishap to avoid.

But even so, it bears repeating: do not ever substitute one for other because they are never interchangeable.

 

Key Takeaways

If your rifle seems to work fine, and optimization seems unnecessary, the best advice may be to stick with what you’ve got.

Ultimately, it takes some experimentation to figure out which combination works best in your rifle, for your needs.

Added weight in the buffer can improve performance, and an H2 buffer with an extra steel and tungsten weight might give you the widest range of options to find the right balance.

One Last Tip

If there’s anyone that knows the AR-15 platform, it’s the US military. As a special offer for our readers, you can get the Official US Army Manual for AR-15/M4/M16 right now – for free. Click here to snag a copy.

19 thoughts on “AR-15 Buffer Weight (and Why It Matters)

  1. I’m trying to find the shortest ar-pistol buffer tube, that uses the carbine buffer? All I need is the tube, I don’t need a new spring an buffer! Who would be recommended for this possible purchase?

    1. maybe sb tactical buffer tube.

  2. Battle arms development

  3. “A heavier buffer takes longer to move, slows down more quickly”.

    Please explain.

    1. they are referring to acceleration. More mass equals slower acceleration

    2. Due to the mass involved it will take more gas pressure to move the buffer, and since the spring is impeding the buffer movement it will stop sooner and return to battery. The amount of time required is based upon the original length of the gas pulse, which is based upon the gas tube length vs Bbl length. If you have 4″ of Bbl after the gas port you get a specific duration of high pressure. Change the Bbl length OR the bullet weight and you change the “dwell time” of the HP pulse. In a 9mm pistol that short strokes using 115gr bullets you can often get improved performance by changing up to 124gr bullets to increase the HP dwell time by the few micro(nano)seconds needed to complete cycling the slide and ejecting/loading the next round. The same applies to any gas operated firearm, whether blowback, direct impingement, or piston activated. Timing issues apply to them all. That’s why there are so many different buffer weights and lengths and springs available. (Springs come in different weights too) Hope this helps.

  4. I built an AR-9 platform “pistol”. Using a Spikes AR-15 lower, and 10.5 ” Foxtrot Mike [FM] 9mm upper.
    On FM’s recommendation, I purchased a 6.4 oz. buffer weight for the spring assembly in the adjustable stock. This weight for the spring (6.4 oz.) was recommended because my 9mm pistol build is “blow-back”, and not gas-assisted.
    My question is this!
    If I purchase a 5.56/.223 (Wylde), 16″ barrel,…will the 6.4 oz. buffer enhance, or deter from performance?
    And will it matter if the 5.56/.223 Wylde has a shorted gas tube,…or a longer one?
    [I was looking at some BCM uppers]

    Any comments or suggestions would be greatly appreciated!
    Thanks!
    Mike

  5. AR 15, 16 inch barrel in .450 bushmaster. With a 2.8 oz. buffer. Problem is it will not feed off of the magazine. The spent cases eject out at 1-2o’clock. The cartridge is jammed at a 45 degree angle, nose up. What buffer would you suggest? It seems that it cycles faster than the magazine can act .

    1. Ken,
      I would think you are actually under gassed with what you are describing. You have a very light buffer for the .450. I would tend to think you would be slamming the bolt back with each shot but it appears the opposite is occurring. You are getting light ejection and the bolt is not going back far enough to catch the next round. I would also expect the bolt will not lock all the back after the last round is fired. So…IMO…your buffer spring is too heavy or you are under gassed or shooting low velocity rounds. Hope this helps.
      Toby

      1. As Toby suggested, the bolt should lock back after the last round is fired, if it doesn’t it’s under gassed. To correct mine I had to drill the gas port slightly bigger to get my 450 to cycle properly. This will be trial and error until you get it to cycle properly, remove the gas block and using wire drills find the smallest size that won’t go in the hole then drill the hole to that size reassemble and try it, if it cycles properly you’re good to go if it doesn’t repeat until it cycles properly, if you drill the hole too big and it’s over gassed put an adjustable gas block on it to tune it.

        Mine is a 450 carbine, H2 buffer (if I remember correctly), with a standard carbine buffer spring.

    2. Ken,

      I am having the same issue. what did you do to resolve the issue?

  6. For an AR-10 which short strokes, does it need a heavier buffer or lighter?

    1. Fred, give us more information on your AR-10 setup? My 20″ AR-10 has been flawless running a rifle length buffer system.
      That said other issues may be causing your short stroke issues. Gas port or gas block obstruction, gas leakage, bad gas rings on the bolt?
      You can try a lighter buffer but the problem probably lies in your gas system.

  7. I have an MGI hydra package 001 that has the conversion kit from 223/5.56 to 300aac to 9mm to 7.62×39 as well i have added the franklin arms binary trigger im having problems with the 9mm getting jammed at 45 degree can anyone suggest best opinion for buffer and weight that will work for everything haven’t tried the other 2 calibers yet but definitely a fun gun to shoot

  8. I have a ar15 that is not locking back after the last round is done it extracts the bullet ok but will not lock back I think it might be my buffer and spring will be possible to try a lighter buffer and spring ro see I’d ir would help

  9. I take issue with this assertion: “The impact of the gas charge of a .458 SOCOM with a muzzle energy of 2,700 ft. lbs. greatly exceeds that of .223 (1,200 ft. lbs).” No, it really doesn’t. While there is more powder being burned, that doesn’t necessarily translate into more port pressure, because the larger bore also has a larger expansion ratio– in which case the port pressure likely will drop. And of course, the pressure curve of the powder also matters.

    The big bores definitely have more recoil momentum and energy. But that’s not the same as having more “gas charge” which they likely do not, because the port sizes will be chosen to keep port pressures in the same range as the 5.56 and thus the buffer and cycling action cannot distinguish between them.

  10. Will a ar 5.56 carbine lenght with 16″ barrel use the same buffer as, say, the same ar with a 10 1/2″ or 12 1/2″ barrel..

  11. What set up would you use doing a NON FIXED regular 6 position tube and the gun has an 18″ bbl. with a rifle length gas system? ??

  12. Simply increasing the buffer weight of the reciprocating mass on your AR 15 can provide noticeable benefits, including reducing felt recoil and muzzle movement and providing additional mass to aid feeding during the loading cycle.

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