AR-15 Brass Ejection Patterns: Diagnosing Your Rifle’s Performance

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5 minute read

As an AR-15 owner, have you ever closely observed the spent brass ejecting from your rifle? The path and angle of that flying brass can reveal a lot about the inner workings of your firearm. Mastering the art of “brass watching” is a key skill for any AR enthusiast looking to optimize their rifle’s performance and it’s not just some YouTuber showboating BS. There is real science to it and it’s easy!

Understanding Ideal AR-15 Ejection Patterns

Put yourself in an aimed position and in an overhead view. Using clock terminology your muzzle is 12 o’clock and your back is 6 o’clock. The perfect AR-15 ejection pattern sees brass flying out around the 3-4:30 o’clock position, relative to the shooter’s position. This indicates your gas system is properly tuned, your buffer and spring are balanced, and your extractor is in good shape. With each shot, you’ll see those shiny casings flying with authority, landing a few feet to the right of your firing position.

AR-15 Ejection Patterns

Identifying AR-15 Ejection Pattern Issues

If you notice your spent brass consistently landing in different zones, that can be a telltale sign of potential problems:

  • 12 – 2 o’clock: This “overgassed” AR-15 ejection pattern is caused by excess gas pressure, pushing the bolt carrier group back with too much force. To fix this, try a heavier buffer spring and/or buffer. On top of that an adjustable gas block would be recommended especially if a suppressor is being tossed in the mix.
  • 5 – 6 o’clock: An undergassed rifle results in a weak ejection, with brass falling short between 5-6 o’clock. Upgrade to a lighter buffer spring and/or buffer to provide more rearward force. It should be noted that if you assembled your gas system it would be advisable to double-check your gas block position before going out to buy things to help with the problem.

We have touched on gas systems and buffers in some of our in-depth articles! You can find them in the links below:

AR-15 Brass Deflection Patterns: Diagnosing Your Rifle's Performance

Factors Affecting AR-15 Ejection Patterns

A variety of components can influence your AR-15’s brass deflection:

  • Gas System: Properly tuned gas flow is crucial for consistent ejection.
  • Buffer Weight: The lighter the buffer the faster the bcg will unlock and move to the rear.
  • Buffer Spring: The spring strength affects how the bolt carrier group cycles.
  • Extractor Strength: A weak extractor can cause unreliable case extraction.
  • Ammunition: Different loads may produce varying ejection patterns. Hotter ammo may overgass and lighter loads may result in undergassed conditions.
  • Suppressor Use: A suppressor will add gas to the system often overgassing a standard build.

Optimizing Your AR-15’s Performance

By closely observing your rifle’s brass deflection, you can diagnose potential issues and make targeted adjustments. This might include:

  • Tuning the gas block to adjust the gas flow
  • Experimenting with different buffer and spring combinations
  • Inspecting and maintaining the extractor for reliable extraction
  • Trying various ammunition types to find the best match for your gun
AR-15 Brass Deflection Patterns: Diagnosing Your Rifle's Performance

Runnin Right: Optimized AR-15 Ejection

Mastering the art of “brass watching” is an essential skill for any serious AR-15 owner. Pay close attention to those spent casings – they just might hold the key to unlocking your rifle’s full potential. In the meantime, if these issues persist while waiting for different parts a rundown on clearing jams may be in order. We have covered this in detail in our How to Use an AR-15: A Beginner’s Guide to Operation and Controls article.

AR-15 Brass Deflection Patterns: Diagnosing Your Rifle's Performance

FAQ

Can brass deflection patterns indicate a worn extractor?

Although a worn or broken extractor can cause odd and inconsistent ejection patterns it is often the last possible issue. Worst case a busted extractor is easy to spot.

What’s the difference between ejection patterns and extraction issues?

Extraction issues usually pop up in the form of jams and malfunctions before affecting ejection patterns.

How do I adjust my AR-15’s gas system?

As most AR firearms sit they are not adjustable. It will require an adjustable gas block or even a buffer with different weights.

Can different ammo change my AR-15’s ejection pattern?

Yes! A higher power cartridge may yield more gas whereas a slower velocity one may cause short strokes or undergassed ejection patterns.

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.

5 THOUGHTS ON "AR-15 Brass Ejection Patterns: Diagnosing Your Rifle’s Performance"

  1. Gugle Delray

    Can changing the trigger components change the gas level and casing ejection?

    1. Hello!

      Changing out trigger components will have no baring on gas levels or ejection patterns. This is typically relegated to upper components such at the BCG and Gas system. The buffer system in the lower is the olnly thing that can use a tune up where that stuff is concerned.

      Hope this helps!

      – AT3 Team

  2. jeffbryan330

    i have a 6.5″ 300 blk out i can shoot 147gr and it runs flawlessly i put 200gr thru it and it wont pick up the next round its ejecting at the proper 3 to 4:30 the buffer that it has is 2.975 oz shoot 1 rd have to rack another rnd in to it proper ejection very confused please help
    thank you
    jeff bryan

    1. Hello Jeff!

      Had a powow with the rest of the team and given this unique situation we came up with the following:

      1. First check what your magazine is. If we are working with an ordinary M2 or M3 PMAG they tend to have feeding issues with heavier grain weights of 300BLK. This is why Magpul makes 300BLK specific magazines that work with all grain weights. So check the mag and try a different one for an affordable testable first step.

      2. If the magazine is not the issue we should turn our attention to the buffer system. We understand that the ejection pattern is ideal. With slight adjustments it should be able to remain in the ideal range and still function. We would suggest to moving to an adjustable buffer in order to dial things in or one step heavier in order to better troubleshoot.

      3. Lastly if those two options do not pan out it may be a barrel/gas system issue. Pehaps a technical issue with the gas block or gas port. This however is pretty unlikely if everything works fine with one grain weight of ammo.

      Closing thoughts:

      – If it is short stroking then the ejection pattern could still hypothetically fall in a near ideal range but this would not make a lot of sense given the already light buffer (unless you have a hefty spring we do not know about). This would be a gas system issue.

      – If the bolt is moving so fast that it returns before the magazine has time to toss up another round then the ejection pattern would likely demonstrate overgassed symptoms. This would be where the brass would be going in front of you. This would be a change to a heavier buffer and a mag change if it wasn’t the right kind. Or an adjustable gas block at the very least.

      Without having the gun right in front of us and seeing the issues in person it will always be tough to diagnose. Our suggestion would be to follow the breadcrumbs in those first three points. Please let us know if you have any other questions and feel free to reach out to our customer service as well.

      Hopefully this was of some help.

      Safe shooting!

      – AT3 Team

  3. Proper BCG speed is the key. I had a pistol length 300 BO that ejected to 5:00 no matter what I tried. I installed an adjustable block and left it open. Talking to the manufacturer we decided it was over gassed to the point the bolt was moving forward before the empty completely cleared and the bolt was bouncing the case off the front of the ejection port. Tuning the gas down solved the problem.

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