Diagnosing firearms problems using the 8 step cycle of operation. Craig Hutchinson, Travis County Sheriff’s Office, Austin, TX Firearms Instructor and Armorer 99% of repeating firearms utilize the 8 step cycle of operation. These steps are: 1. Feed 2. Chamber 3. Lock 4. Fire 5. Unlock 6. Extract 7. Eject 8. Cock Feeding. Whether the weapon uses a detachable box magazine (AR-15, AK-47), a tubular magazine (many shotguns and .22 rifles), a cylinder (revolver) or manually loaded (break open shotgun) the round must feed into the chamber at the proper angle, proper depth at the proper time for this step to be considered a success. Broken, cracked or misaligned magazine feed lips impair proper feeding. Broken, bent or fouled shell stops in tubular magazine weapons wreak havoc on proper feeding. Your own fingers or speed loaders are the feeding devices for revolvers just as your fingers feed the break open shotgun. Chambering. Once the round leaves the magazine and is aligned with the bore, it can chamber. As long as the round and the chamber are to specs, this step should go smoothly. An overly fouled chamber can prevent proper chambering. An out of spec round of ammunition can fail to chamber. A malfunction at this point is often related to the feeding. If the ammunition did not get started off correctly in the magazine, it likely will not chamber correctly. Locking. The breech generally must lock (close completely) before the next step can take place. If the round did not fully chamber, the breech will not lock. As above if the chamber is excessively dirty or there is an ammunition issue the breech cannot lock. Fire – Broken firing pins (strikers) are very rare as are broken firing pin springs or hammer springs. If a round will not fire it is generally because the breech is not fully locked. Most firearms have a failsafe designed in that will not allow it to fire with the breech unlocked or partially locked. Because of the high pressures involved and the nature of the cartridge case, hot gasses will likely escape causing injury if the firearm is allowed to fire with out being fully locked. Out of battery discharges are usually catastrophic events requiring medical attention Unlock. Generally speaking if the gun will not unlock, something has gone very wrong during the firing sequence. Excessive pressures and/or broken parts are the most common culprits. Excessive pressures can cause metal to flow into crevasses and then prevent the firearm from unlocking. Primer material flowing into the void between the firing pin and its hole in the breech block/bolt/slide can prevent unlocking. Broken cam pins on AR-15’s can cause this. Broken links on 1911’s can happen as can broken slide stops on most Semi-Auto pistols. Extract. The extractor must pull the spent case out of the chamber in order to proceed to the next step. Extractor hooks can fail and break. Extractor springs can fail or become weak. The rim of the case can shear off leaving the case in the chamber. Extraction is a violent action that must take place at the appropriate time to be successful. Too early and the pressures are excessive. Too late and there is insufficient pressure to overcome the recoil spring tension. Eject. The ejector can be a spring loaded pin/plunger that is contained in the breech bolt (AR-15, Remington 700) or a projection within the receiver (AK-47, most pump shotguns and Mauser rifles). Ejection is rarely a problem as it is a relatively simple operation. As long as the extraction process went well, the ejection process should go well. Cock. You just can’t miss the big cock at the end. Cocking can take several forms. It can be pressing the hammer back to a rearward position (1911, AR-15, AK-47) it can be accomplished by rotating the bolt to unlock (Large Ring Mauser). It can be closing the bolt (Small Ring Mauser). It can be the action of hinging open the action on a double barrel shotgun. If the gun fails to cock (or remain cocked), generally you have a malfunction that cannot be corrected in the field w/out tools and spare parts. When a weapon experiences a malfunction, generally the cause is located one step before the step in which the malfunction becomes apparent. If the round fails to chamber, it is likely a feed problem (usually related to the magazine). Replace the magazine and continue. If the weapon fails to fire it could be because it is not locked into battery. Check to insure the ammunition is not the cause. If the ammunition is in specs the cause could be fouling, lack of lubrication, or rarely a broken firing pin/spring or hammer/striker. Ejection problems are normally as a result in the extraction step, etc. If one understands how a gun works, it is much easier to understand why it does not work. If you look for the cause of a malfunction, look at the previous step for the explanation.