FBI 1076 Pistol Lockup
There has been much discussion over the years as to the cause of the reports (five or less) of FBI 1076 lockups and other FBI issues with the pistol. The following description comes directly from an internal S&W document authored by a S&W engineer sent to upper management at S&W. The date is unkown.
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"The descriptions of the pistols which locked up in Miami and Tampa were identical. The hammer was in the half-cock position; the trigger was fully forward with no freedom of movement; the hammer could not be fully cocked, and the rearward travel of the slide was limited by the hammer. Both pistols were reloaded just prior to the lockup.
It has been determined it is possible for the drawbar to be lifted and locked in a position that prevents trigger movement. Once in the locked position, neither the trigger nor the drawbar are free to move. Therefore, the slide can only move to the point where the hammer makes contact with the drawbar. Only with the hammer in the 1/2 cock position, and even then the possibility exists only on a small percentage of limits, is the drawbar free to be put into a locked position. The force that lifts the drawbar into the locked position is the top round of the magazine during loading.
This lockup is not possible with other S&W pistols in that the special FBI trigger has a different interface where the trigger, the trigger play spring and drawbar intersect. On standard S&W triggers, the area of the trigger that is causing the lockup has been removed.
A simple test has been devised to determine whether or not a pistol can possibly be locked up. This test is performed with the pistol field stripped and the hammer in the 1/2 cock position. To test the pistol, you simply push the drawbar forward and up. Then pull the trigger. If you cannot move the trigger, it is possible for the pistol to be locked up. Even then, it would require a round to be very far forward in the magazine to actually contact and push up the drawbar.
There appear to be two possible product changes to prevent a pistol from locking up. First, the current trigger can be modified to add 0.010" of material to the front stop surface. This added material changes the relationship between the trigger and drawbar in a way that prevents the two parts from ever getting into a lockup condition. The second solution is to change back to the standard trigger used on all other S&W pistols. Further testing is still required to insure that this solution has no negative tradeoffs.
To verify the effectiveness of both solutions, the FBI trigger with 0.010" added and the standard trigger, are not sensitive to wear, endurance tests were conducted for both configurations. Contact is made between the trigger and drawbar in the FBI configuration. No contact exists between these parts in the standard trigger configuration. Therefore, four pistols were endurance tested with the FBI trigger and only one with the standard trigger. The four pistols with FBI triggers were fired 5,000, 10,000, 15,000 and 20,000 rounds. The pistol with the standard trigger was fired 20,000 rounds. No wear on the critical surfaces was seen after the test. None of the five pistols could be put into the lockup position after the endurance test.
II. CHIPPED EXTRACTORS
As we have previously reported, the cause of the chipped extractors was the processing of this part. A small burr was being generated during machining and became brittle when the part was hardened by heat treatment. The correction was in reprocessing the part to eliminate the burr.
Parts have been made to the new process and test fired. Six pistols were test fired with new extractors. The number of rounds fired through each pistol are:
1 pistol 36,000 rounds
2 pistols 20,000 rounds
1 pistol 15,000 rounds
1 pistol 10,000 rounds
1 pistol 5,000 rounds
No chipping or any other damage was seen on any of the six extractors. These parts are available for inspection.
III. CRACKED MAGAZINE FOLLOWERS
The test procedure used to determine which material should be used in the magazine follower was described in our previous letter. In addition to these tests, we have loaded and fired 100 magazine assemblies 100 times each with no damage to the follower. An automated machine was developed to slam both loaded and unloaded magazines into a frame. This machine has been used, and did not fracture the new follower after 50,000 cycles.
IV. BROKEN TRIGGER PLAY SPRING
Trigger play springs had been breaking after approximately 1,500 rounds during training at Quantico. Prior to the spring actually breaking, it was frequently observed that one or both of the legs, which contact the trigger, had been severely bent rearward.
The first action taken to improve the durability of this part was to increase the amount of clearance between it and the pistol frame. This was done to assure no contact between these two parts under any condition. When the clearance cut in the frame was increased by 0.020" on each side, the severe bending of the spring was eliminated and the durability increased to approximately 3,000 rounds.
After exploring and discounting stress resulting from thermal cycles, die wear, and improper processing, it was decided to decrease the stress level in the part by making it more flexible. This was accomplished by increasing the length of the two slots in the spring and decreasing the material thickness from 0.008" to 0.007". Alternate materials were also investigated but none proved superior to the 301 stainless now used. The combination of the increased clearance cuts in the frame and new trigger play springs have been 100% successful in five pistols. The number of rounds fired are:
2 pistols 20,000 rounds
1 pistol 15,000 rounds
1 pistol 10,000 rounds
1 pistol 5,000 rounds
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