There are three recoil action types. The three styles being Long, Short, and Inertia. All three are similar in that they rely on the recoil energy produced by the ammunition source to cycle the action. Recoil Actions function similarly to a blowback action. The primary difference is that with blowback action types the bolts do not lock (whether straight or delayed) whereas all recoil action types utilize a locking bolt of one type or another.
Understanding that we now need to differentiate the different operation styles of the three and even identify a few unique troubleshooting procedures specific to the sub-type. Let’s first start by explaining each Recoil Action type.
Long Recoil Action:
For long recoil action, the barrel and bolt move as a unit to the rear of the cycle. At the end of the rearward movement, the bolt catches (locks) and is held as the barrel returns forward. During the transitional movement, the spent casing remains attached to the bolt via the extractor. As the barrel continues forward, an ejector attached to the barrel extension will eject the spent cartridge. When the barrel returns to the full forward position, the bolt is released and closes the action while chambering the new round and finally locking into the barrel for the next shot.
Short Recoil Action:
Short Recoil is the primary action utilized in most semi-automatic pistols. In the case of short recoil actions, the barrel and bolt only travel together for a ‘SHORT’ distance until they unlock. At this time the barrel abruptly stops its travel as the bolt continues along the cycle compressing the recoil spring until it hits the most rearward point. During this rearward movement, the bolt extracts and ejects the spent cartridge as well as readies the next round for feeding. As the bolt moves forward once again, it will pick up and chamber the next round while also forcing the barrel back to its forward position and locking both together with a round chambered for the next shot.
Inertia Recoil Action:
The Inertia Recoil Action is a unique style of its own. The most unique feature with the inertia style is that the bolt body and locking head are connected with a stiff spring between the two. This is the heart of the inertia design. Upon firing the system recoils as a unit. The bolt for a split second remains stationary as the locking head is forced into it by the recoil and compresses the inertia spring. As the energy is transferred and the inertia spring begins forcing the bolt rearward the locking head rides through a channel in the bolt forcing it to twist and unlock from the barrel. Once unlocked the locking head travels rearward through the cycle with the bolt (attached) extracting and ejecting the spent cartridge along the way. Once they hit the full rearward position, they are then forced forward by the recoil spring feeding and chambering the next cartridge during the cycle. Finally, the bolt forces the locking head into the chamber in a locked position, and the weapon is ready for the next shot.
Identifying the action type (recoil) is a good first step in diagnosing malfunctions, however further identifying which subtypes are necessary as well as the steps in troubleshooting them have some differing procedures. While I’m not going to attempt to cover all of those variables, I will share a quick example below to highlight the point.
Locking Malfunctions: If you’re having locking malfunctions with your firearm the potential culprit parts could vary depending on recoil type. Some of the primary culprits by recoil type are listed below.
LA: Bolt, Locking Block, Barrel Extension
SA: Slide, Barrel, (model dependent) Locking Block, Link, Barrel Pin, and Barrel Bushing
IA: Bolt, Carrier, Cam Pin, Inertia Spring, Barrel Extension
As was discussed earlier in describing the various way these subtypes operate it only makes sense to understand how the particular style of recoil action can play a part in troubleshooting it. The more you come to understand the operation and parts interaction of these (and any weapon for that matter), the easier it will be to quickly identify and repair issues you may come across.