AR 15 ejection pattern says a lot about the amount of gas the rifle is currently exerting. The direction of the shell coming out of the ejection port hitting the deflector is the indictor of too much gas or too little assuming we are only using standard target ammo.
Ejector spring tension, ammo powder charge, buffer spring, deflector angle, gas port size, bolt carrier group weight, buffer weight, suppressor all play a role. There are many permutation of configurations a user can play with.
Common problems we can see from the ejection pattern can lead to malfunction are:
- Over gassed
- Short stroking
Ejection Pattern Direction
The ideal ejector pattern begins around 3:00 to the 4:30 position.
We will use a clock to illustrate this.
The place where the shell comes out is right in the middle of the clock. The back part of the gun points to the bottom, where the 6:00 is. Most people think that used bullets should pop out between where the 3:00 and 4:30 numbers would be. But sometimes, they pop out between the top (12:00) and the 3:00. Other times, they come out between the 4:30 and the 6:00.
If a gun has its ejection port on the right side, it can't push things out between the bottom (6:00) and the top (12:00).
Over Gassed AR15
An over gassed AR15 can cause:
- Feeding issue
- Over time damage to the bolt carrier group
- Bolt slamming back too hard
- More than usual recoil
- Forward ejection pattern
The AR-15's gas block manages its gas pressure. At the gas block, the system gathers and channels this pressure to the upper receiver and bolt carrier group.
While most AR15 gas blocks are fixed, and the only thing you can tweak is the rest of the gun.
With an adjustable gas block, you can achieve the perfect pressure setting for improved timing, experience reduced carbon accumulation, and avoid undue wear and tear. Moreover, it can produce an ejection pattern between 12:00 and 3:00.
Short Stroking
If the shell ejection pattern is past the 4 o'clock position, it's an indication of short stroking, aka not enough gas pressure. In the physical sense, the bolt isn't traveling back enough, and the shell isn't bouncing off the deflector enough either.
The shooter can increase the pressure with an adjustable gas block. A heavy buffers and springs often cause short stroking because it's applying resistance tension against the bolt when it's coming back. If you switch to a lighter buffer or spring, it lets the bolt and carrier move fully to the rear when firing.
Cleaning The Gun
Be sure to clean the gun too. Friction on moving components can make the rifle exhibit symptoms of short stroking. So keep the rifle cleaned and well lubricated make all the parts move freely to prevent malfunction. Short stroking happens when the gas rings on the bolt carrier group aren't staggered or the gas tube is clogged with carbon residue.
Use a strong CLP like the Breakthrough carbon remover to break off these carbon residues.