{"id":23032,"date":"2020-01-26T21:37:59","date_gmt":"2020-01-27T03:37:59","guid":{"rendered":"https:\/\/gunmagwarehouse.com\/blog\/?p=23032"},"modified":"2026-01-13T12:57:40","modified_gmt":"2026-01-13T18:57:40","slug":"ar15-firearm-tuning-the-buffer-on-a-12-5-in-build","status":"publish","type":"post","link":"https:\/\/gunmagwarehouse.com\/blog\/ar15-firearm-tuning-the-buffer-on-a-12-5-in-build\/","title":{"rendered":"AR15 Firearm: Tuning the Buffer on a 12.5 in. build"},"content":{"rendered":"

Note: You may notice a change in this article. It originally was an article about tuning the buffer on my AR15 Pistol. I have never claimed to have all the answers and in this case, the answers I thought I had were incorrect. As in many parts of my life, I learn from others and in this case, you, the readers tipped me off to my error. The error is one of legal semantics and it is unfortunate that we all have to deal with these silly rules, but we do. I have amended the post below to reflect accurately that my 12.5″ AR is, in fact, a firearm and not a pistol.<\/span><\/em><\/p>\n

When it comes to defensive or duty firearms the most important attribute is likely reliability. When you choose a gun as a life-saving tool you need to know it will fire when you need it to: in other words, on-demand, not on command<\/em>. In an AR15, the gas system is one area where reliability can be a make it or break it set of components and the most variable aspect of the gas system may very well be the buffer. It is for this reason that I paid close attention to tuning the AR15 buffer as I completed my AR pistol build.<\/span><\/p>\n

It turned out to be a far simpler process than I expected. I feel comfortable that anyone who can assemble an AR15 can easily tune their buffer, especially with the right AR15 tools. <\/span><\/p>\n

\"AR15
The contents of the H3 buffer look similar to the carbine buffer, however, the weights are tungsten and have significantly more mass than the carbon steel buffer weights.<\/figcaption><\/figure>\n

AR Firearm: Why I decided to build now<\/span><\/h2>\n

A couple of months back I looked at the prices of AR15 components, especially lower receivers, and decided it was time to make sure I had all the components I needed to build whatever tools I wanted for the next few years. <\/span>Prices were so low that I couldn\u2019t conceive of them getting much lower and I was able to capitalize on some special deals, including a couple offered through <\/span>Aero Precision (aeroprecisionusa.com)<\/span>. Among those were four<\/span> “blem” M4E1 Enhanced lowers,1 for my build and one for my wife and two daughters.<\/span><\/p>\n

My AR15 build: a quick overview<\/span><\/h2>\n
\"AR15
I primarily selected Aero precision components to avoid tolerance-related complications that will sometimes arise when mixing brands.<\/figcaption><\/figure>\n

It wasn\u2019t long before I started to collect the other parts I needed. I already had a complete bolt and bolt carrier and an ALG Defense ACT trigger, but otherwise decided to keep my build relatively “on brand” to avoid issues with tolerance stacking. Aero knows what Aero builds so I expected the parts to work together.<\/span><\/p>\n

12.5″ AR Build Gas System<\/span><\/h3>\n

I decided on a 12.5 in. barrel and handguard mounted to the Aero M4E1 Enhanced upper receiver. The barrel has a gas port at carbine length. I added a carbine length gas tube and an Aero gas block to my cart.<\/span><\/p>\n

Carbine length made sense for the gas system because it has about the same dwell time as a 16\u201d mid-length gas system. Dwell time is the length from the gas port to the muzzle and is important because it is when gas is forced back into the bolt to operate the action. I have found the mid-length system to be very reliable in my JP VTac AR15 and I approached my decision from an \u201cif it ain\u2019t broke, don’t fix it view.\u201d<\/span><\/p>\n

It should also be noted that the gas block I selected is not an adjustable block. An adjustable block would provide more wiggle room, but I was building for reliability and simplicity. In addition, the gas block is easy to swap out in the future if needed.<\/span><\/p>\n

Other Pieces, Parts, and Paraphernalia<\/span><\/h3>\n

I sourced my lower parts kit, grip, and pistol brace from a distributor taking advantage of wholesale pricing. This is also where I grabbed a Spike\u2019s Tactical H3 buffer. <\/span><\/p>\n

Why the AR 15 Buffer Matters<\/span><\/h2>\n
\"AR15
Disassembly of the carbine buffer. I use a special little block I drilled out and a roll of electrical tape, one of my favorite smithing tools.<\/figcaption><\/figure>\n

The buffer has an important job. Along with the buffer spring, the buffer provides resistance to the action of the AR as it moves rearward after a shot has been fired. The buffer\u2019s job is to help slow the BCG down so that it doesn\u2019t damage the rifle (in this case, firearm<\/em>) over time and to help the rifle\/pistol\/firearm feel like a soft shooter.<\/span><\/p>\n

If the buffer is too light it can travel to quickly and batter the bolt carrier group and the buffer tube. If the buffer is too heavy, it can slow the BCG to the point where it doesn\u2019t move enough to eject the fired round, scoop a new round from the mag, or press the bolt firmly into battery.<\/span><\/p>\n

After a build is complete tuning the buffer is the easiest way to modify bolt speed.<\/span><\/p>\n

Other Gas System Factors<\/span><\/h2>\n

Don\u2019t think for a second that the buffer is the only way to tune the gas system of an AR15. It isn\u2019t. It is the easiest way to tune the gas system after a build is complete. There are other options but each is more of a commitment and could still require the buffer to be tuned.<\/span><\/p>\n

Gas System Length<\/span><\/h2>\n

This is probably one of the biggest factors in how an AR works so it makes sense that changing the length of the gas system would change performance. The problem is changing the length of the gas system requires changing a barrel. The physical act of changing a barrel is easy enough if you have the right tools. The problem is the cost. Good barrels aren\u2019t cheap so this should normally be viewed as the last resort. Choose wisely upfront.<\/span><\/p>\n

Know that changing a barrel can also result in a larger or smaller gas port or simply a better match between the gas port and gas block. These factors are harder to control.<\/span><\/p>\n

Gas Block<\/span><\/h2>\n

Changing to a different or an adjustable gas block is an option for tuning. This isn\u2019t too tough, but would require the removal of the hand guard.<\/span><\/p>\n

Changing the gas block may simply provide better alignment or a larger port in the gas block itself.<\/span><\/p>\n

BCG Weight<\/span><\/h2>\n

Bolt carrier groups can be made out of different materials or have material removed so that their mass changes. A lighter or heavier BCG can significantly change the speed the carrier is traveling and reliability. Changing the BCG is actually the easiest mod you can make to the system, but bolt carrier groups aren\u2019t cheap. It could get expensive quickly trying to tune the BCG.<\/span><\/p>\n

Tuning the Buffer<\/span><\/h2>\n
\"AR15
Here you can see the contents of this carbine’s AR15 buffer: 3 carbon steel weights and 3 rubber spacers.<\/figcaption><\/figure>\n

Tuning in your AR15 buffer is pretty darn easy and it can be the most cost-effective way to increase the performance of your AR.<\/span><\/p>\n

If you can pound in a nail you can disassemble a buffer.<\/span><\/p>\n

What you are looking for.<\/span><\/h2>\n
\"AR15
I selected a Spike’s Tactical T3 buffer as my tungsten weight donor. It was the most affordable H3 buffer I could find.<\/figcaption><\/figure>\n

You have properly tuned your buffer when you observe the following while shooting the first few rounds of a full magazine:<\/span><\/p>\n