Diagnosing a Failure to Feed *Video* AR-15 or AR-10


Credit to Dr. Ryan Terry, DDS (aka “Doc”) for the Failure to Feed Video above.

While working on an AR-308 rifle for Mr. Man, I ran into a failure to feed problem. The rifle was consistently inconsistent when it came to its ability to properly feed rounds from the magazine into the chamber. It might fire a round or two just fine, but would always end with the bolt slamming down on the side of a live case.  The brass would be smashed and deformed rendering the round unsafe to fire in most cases.

Every now and then, I’d get the bolt closing with no round in the chamber, and live rounds still in the magazine.  Another obvious symptom was that the brass had scratches, and sometimes gouges cut down the length of the case.  As I’ll explain later, this was from the bolt scraping down the length of the cartridge when trying to feed the next round.


An example of my failure to feed.

Luckily, I’d run into this problem before, and was able to recognize it for what it was, diagnose the problem, and begin to systematically eliminate the cause, one component at a time until the problem was resolved.

Short Stroking:

As you can see from the video above the rifle was “Short Stroking.”  I know, I know…Short Stroking sounds like a midget having a good time in Tijuana, but it’s actually a pretty annoying problem.  It’s caused when the gas system doesn’t have enough pressure to blow the bolt all the way to the rear, and thus can’t effectively cycle the next round.  The bolt does not clear the back of the brass case.  Thus, the bolt face is unable to catch the lip of the brass, and push it up the feed ramps and into the chamber.  When the bolt reaches the end of its rearward travel, the buffer spring and buffer push the bolt forward toward the the muzzle.  The bolt face runs rough shot over the brass case being held in position by the magazine.  Sometimes, the bolt just grinds over the brass, leaving a tell tale scratch and an empty chamber.

However, most of the time, the friction of the bolt face on the brass has enough force to dislodge the round from the magazine, but the bolt is not properly positioned at the rear of the case, so instead of it feeding the round into the chamber, it slams closed on the side of the brass leaving it wedged in the upper receiver with the nose of the bullet wedged in the barrel’s lugs (see picture above), and leaving the rifle out of battery.

To clear the problem you have to dump the mag, hold the bolt back, and sometimes sweep the inside of the upper receiver to dislodge the stuck case.  This is quite annoying on the range, but in self defense situation it can be deadly.

How to Test for Short Stroking:

This couldn’t be simpler.  Load one round in the magazine, and fire it.  If the bolt locks to the rear, and holds open, then your rifle is not short stroking.  Look for alternative explanations as to your malfunction.

If however the bolt is closed, and the firing of the round did not cause it to travel a sufficient distance to the rear in order to reach the bolt catch, then you have a short stroking problem. Voila!

How to Fix the Short Stroking Problem:

Try each of the following one at a time until the problem is fixed.  Don’t try to do them all at once, or you will never know what the real problem was.

  1. Clean your Gun, Dude.  When attempting to fix any problem, you should always start with the most simplistic, and obvious first.  So….Clean your damned rifle.  Yep, you’d be surprised how often this will fix problems especially with an auto loading firearm. I know this seems like an obvious thing, and it is, but it could have fixed many of the problems that caused lots of friends to bring me their firearms that are acting up.
  2. After cleaning, lube the crap out of the bolt.  Especially many AR-10 type rifles (which is what is seen in this article) have to be run very wet.  AR-15’s run with no lube can have too great of friction, thus causing the bolt to fail to travel all the way to the rear.  Especially when breaking in a new upper receiver, and BCG that hasn’t worn any of the rough finish off yet.   Friction is not your friend here.
  3. Realign the Gas Block.  Especially if the barrel does not have milled out holes for the gas block.  I’m OCD about how I align the gas blocks on the rifles I assemble, but after the barrel and block heat up, things can walk a little bit.  This causes the hole in the gas block to become misaligned which prevents gas from traveling down the gas tube, and into the gas key on the bolt, allowing it to cycle with each shot.
  4. Inspect gas block to barrel fit, and replace if needed.  If the fit is incorrect, and gas is allowed to escape between the barrel and the gas block, then you will not get the pressure you need from the expanding gas being directed down the gas tube as intended.  If this is the case, then replace the gas block with one that will not allow gas to escape any part of the process.
  5. Inspect and/or replace the gas tube.  Gas tubes are thin material, and can get bent, kinked or even broken causing a failure. They can also get blocked with carbon build up, dirt, or other debris over time.  If any of these are the case, replace the part, and conduct the bolt lock back test mentioned above.
  6. Check the gas key on the bolt to insure that it is properly staked, and you don’t have a gas leak.  This appears to be rare.  It has never happened to me personally, but know others to whom it has happened.
  7. Proper Buffer Spring and/or Buffer.  You can sometimes lighten up the buffer weight to band aid the problem, but usually it is a gas issue, and not the spring/buffer.  Likewise, if you are running an AR-10 type rifle, ensure that you do not have an AR-15 buffer spring (and vise versa).  Unfortunately, nearly all parts of a firearm are perishable, so replace the buffer spring if it’s necessary.
  8. Inspect, and/or replace the gas rings on the bolt.  Again parts wear out, especially after a couple of thousand rounds.  If you’ve got a new rifle (and/or bolt), then look for the problem to fall with one of the other areas.

Which problem did the rifle in the video have?

In my case it was #4 above.  The gas block appears to not have been milled correctly, and was allowing gas to escape between the barrel and gas block, as seen in the pictures below.  FYI, it was a Fulton Armory gas block.  They will be receiving a call.


You can see where gas was escaping from under the gas block.  No Bueno, Senor!



After the installation of an adjustable gas block, we were back in business.  To see the instillation, and a quick review of the adjustable gas block, check out How to Install an Adjustable Gas Block on AR-10 or AR-15 (SLR Rifleworks). See the test results below.  As my dear old grandpappy used to say “it runs like a spotted ass ape.”



Credit to Dr. Ryan Terry, DDS (“Doc”) for the above Slow Mo Bolt Return video.



The information provided herein is for entertainment purposes only.  If you are not 100% sure what you are doing, have a qualified gunsmith work on your firearms.  Remember, it is much easier to remove body parts than to return them to their original form, and function.

Categories: diy, hunting, reloading, Shooting

Tags: , , , , , , , , , , , , , , , , , , , , , ,

5 replies

  1. Great cautionary notes, as always! Excellent diagnostic chart, too!



  1. How to Install an Adjustable Gas Block on AR-10 or AR-15 (SLR Rifleworks) – Greatoutdoordinary
  2. A Definitive Guide to AR-15 Parts and Upgrades - Angela Gallo's Blog

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: