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Posted: 12/24/2011 11:40:50 PM EDT
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There is not enough room for the hammer spring leg to catch the small anchor cut out on the trigger pin to retain it. So when firing the trigger pin walks out. How can I fix this problem? |
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Something else is wrong...the most common cause is hammer spring installed upside down and even though it looks right, it won't engage the groove in the pin correctly.
Refer to the sticky build instructions posted here and make sure the hammer spring is installed correctly and that one leg (depending on which side you put the groove in the pin on) of the hammer spring is engaging the pin. It is possible, but unlikely, that your spring was somehow tweaked and not fitting properly. I have seen the M16/M4 platform fire thousands upon thousands of round w/o a single pin walking, even a little. |
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I'm going with 'upside down hammer spring,' too. (I've done it before, oops!) I'd double check that first. Looked at my other rifle and realized something was amiss. Upside down, the 'leg' of the spring comes down at a bit of an angle vs. right-side-up, making it grab that groove in the pin enough to hold together at first, but not tightly down in the channel at the edge of the trigger where it sits next to the inner side of the receiver. It started walking within 20 rounds. Flipped it around, went and fired 300 rounds, no more walking.
Here is a great pic to use for a comparison. (It's not my pic, so I'm not embedding it.) |
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A Trigger Pin that vibrates out of the lower receiver during firing, is often times referred to as a “Walking Trigger Pin”. “Walking Trigger Pins” are usually the result of two common mistakes made by those new to assembling their own lower receivers involving installation of the FCG (Fire Control Group).
Problem Number One: Hammer Spring Leg Placement Often times the assembler mistakenly places the legs of the hammer spring under the trigger pin, against the bottom of the FCG pocket of the lower receiver along the sides of the trigger assembly. Taking a look at the diagram below, we see that the hammer spring legs actually ride on top of the trigger pin. The pins utilized for the trigger and hammer, are designed with two circumferential grooves, one groove outboard and one center. When a pin is utilized in the trigger position, it is retained within the lower receiver by the tension of one of the hammer spring legs riding within the outermost groove of the pin. (See View A of the illustration below.) If the hammer spring legs are not placed on top of the trigger pin, with one leg placed in the outermost trigger pin groove, the firer may experience a “Walking Trigger Pin”. Problem Number Two: Incorrect Hammer Spring Installation Occasionally lower receiver parts kits (LPK) arrive with the hammer and hammer spring separated from each other. If not following the maintenance manual, or detailed assembly instructions, incorrect installation of the hammer spring by the assembler is often times the result. Or, there was a mistake during assembly of the two by the distributor or Mfr., resulting in incorrect installation of the hammer spring. Taking a look at the illustration below (Position Of The Hammer Spring Legs), we see the correct installation of the hammer spring on the hammer itself. Incorrect installation of the hammer spring on the hammer, can lead to incorrect pressure applied to the trigger pin by the tails of the hammer spring, most critical being the spring tail riding in the trigger pin groove. This lack of proper spring tail pressure, can often times lead to a “Walking Trigger Pin”. A not too common problem, but one which I have personally experienced which can lead to a “Walking Trigger Pin”, was caused by the grooves not being cut deep enough in the trigger pin to sufficiently hold the tail of the hammer spring. In this instance, I had to resort to opening up of the groove, using a small jewelers rat tail file. This was a temporary fix. Removal and replacement of the trigger pin with an in-spec trigger pin would be highly recommended.  |
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My Ruger SR556 had this issue 'out-of-the-box' called Ruger and they sent me new pins - same problem (and all were installed correctly).
I purchased the Anti-Walkout pin and all is good . Since then I have installed them on all my lowers. I'm all in for reliability - ZERO failure. |
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Quoted: I'm going with 'upside down hammer spring,' too. (I've done it before, oops!) I'd double check that first. Looked at my other rifle and realized something was amiss. Upside down, the 'leg' of the spring comes down at a bit of an angle vs. right-side-up, making it grab that groove in the pin enough to hold together at first, but not tightly down in the channel at the edge of the trigger where it sits next to the inner side of the receiver. It started walking within 20 rounds. Flipped it around, went and fired 300 rounds, no more walking. Here is a great pic to use for a comparison. (It's not my pic, so I'm not embedding it.) Wow! You guys rock. Thanks guys. It was the inverted hammer spring positioning the spring legs wrong. |
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