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Old March 25, 2020, 11:54 AM   #1
ECM4
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AR Hammer Pin is walking out.

Just bought a drop in trigger to put in my AR9. Once I got it all together I was testing the trigger. Dry fired a few times and my hammer pin was about to fall out. What causes this and what is the fix? I have a feeling the holes in the drop in trigger are loose and maybe the trigger is just bad. Anyone ever have this problem? How did you fix it?
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Old March 25, 2020, 12:08 PM   #2
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It should have some type of pin retention.
Check the instructions and check your pins. Make sure they're installed in the correct orientation.
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Old March 25, 2020, 12:15 PM   #3
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Incorrect information removed...
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Old March 25, 2020, 12:30 PM   #4
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IIRC, a self contained drop in trigger group does not allow the hammer spring to hold the pins in. If this is fact one of the “cartridge” type trigger groups. Like the POF units i use, some type of anti-walk pins should be used.
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Old March 25, 2020, 12:56 PM   #5
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Thanks for the info guys. This is the first drop in trigger I have ever used. I will check the retention pins on the bottom that push up against the lower receiver. Maybe I didn’t tighten them up enough. then I can order new hammer/trigger pins if that doesn’t work.
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Old March 25, 2020, 01:17 PM   #6
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Usually the hammer and trigger pins (assuming your drop in re-uses standard AR pins) will be notched with grooves on the ends. Make sure you put both pins in the same orientation, usually there's enough room to slip a thin c-ring to help.
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Old March 25, 2020, 02:02 PM   #7
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Quote:
Thanks for the info guys. This is the first drop in trigger I have ever used. I will check the retention pins on the bottom that push up against the lower receiver. Maybe I didn’t tighten them up enough. then I can order new hammer/trigger pins if that doesn’t work.
Normally those bottom screws should just kiss the bottom of the well. If addressing them doesn't work, redo them again where they just touch (or totally collapse them where they don't touch) and either way, install a set of anti-rotation pins such as KNS.
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Old March 25, 2020, 05:03 PM   #8
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In my guns, the hammer has a spring wire contained in the hammer (there is a groove milled into the center of the bottom radius and a hole extending up into the hammer) that bears against the center groove of the hammer pin when it is installed. That spring wire retains the hammer pin.

The hammer spring legs do rest atop the trigger pin to prevent it walking, but there is no way the forward legs of the trigger spring will go over the hammer pin.

All five of my cartridge type FCGs (three POF, two Rise Armament) came with anti-walk pins, as both pin holes are smooth with no built-in retention.
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Old March 25, 2020, 06:16 PM   #9
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Quote:
Originally Posted by imashooter View Post
Normally those bottom screws should just kiss the bottom of the well. If addressing them doesn't work, redo them again where they just touch (or totally collapse them where they don't touch) and either way, install a set of anti-rotation pins such as KNS.
The pins at the bottom were the problem. Directions said to not over tighten so I barely got them to touch when originally installed. I went back and I torqued them down pretty tight it actually tightened up my hammer pin. I at-least feel comfortable shooting it now but I will just get some new pins to make sure.
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Old March 25, 2020, 06:52 PM   #10
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KNS pins are sometimes viewed as a gimmick... but for the one lower that constantly had the pins walking, I actually toss them on all my lowers for piece of mind.
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Old March 25, 2020, 07:28 PM   #11
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44 AMP is dead on.
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Old March 26, 2020, 02:34 AM   #12
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ECM4, I assume you installed a Timney drop-in hammer/trigger group.

Personality, I wouldn't trust two tiny set screws to hold the hammer and trigger pins in place. KNS pins or similar are the way to go.
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Old March 26, 2020, 07:54 AM   #13
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**clarity**

Thanks
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Old March 26, 2020, 03:12 PM   #14
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Here are some pictures to illustrate how the hammer pin in a standard AR fire control group is retained.

Hammer with spring and pin installed - note the boss and coil over on each side extends all the way to the receiver walls (the pin ends will be inside the receiver walls):


Piano wire hammer pin retainer shown at bottom of hammer


Piano wire hammer pin retainer (Shown inside cut in center of pin tunnel) - wire bears against center grooove of hammer pin and keeps pin in place in receiver


I hope this helps...
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Old March 26, 2020, 03:45 PM   #15
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Simple fix - a single tiny drop of hot glue from glue gun. I did that for a couple of my Glocks and that fixed the problem for good.
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Old March 26, 2020, 05:06 PM   #16
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Quote:
IIRC, a self contained drop in trigger group does not allow the hammer spring to hold the pins in. If this is fact one of the “cartridge” type trigger groups. Like the POF units i use, some type of anti-walk pins should be used.
This
You'll need anti-walk pins for this style, I have used a few varieties, pick one most work fine.
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Old March 26, 2020, 05:19 PM   #17
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Here is a picture from one of my AR's showing the spring legs up over the pin.

I also would just pick up a set of anti-walk pins to be sure the pins don't drop, its cheap insurance in your case.
Attached Images
File Type: jpg FCG 1.jpg (38.9 KB, 23 views)
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Old March 26, 2020, 06:08 PM   #18
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Quote:
Originally Posted by DnPRK View Post
ECM4, I assume you installed a Timney drop-in hammer/trigger group.

Personality, I wouldn't trust two tiny set screws to hold the hammer and trigger pins in place. KNS pins or similar are the way to go.
I installed AAO manufacturing drop in trigger. About the 3rd of the price of a higher end timney. Went out and shot a few hundred rounds through it today and pins never moved. I will be getting some new pins to make sure but nothing can move. For the price these triggers feel great. We will find out if they still work after thousands of rounds down the road but for now can’t be happier with a $90 trigger.
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Old March 26, 2020, 06:28 PM   #19
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Elftman makes the best, IMO. LINK

I use these on all my AR’S.
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Old March 26, 2020, 07:41 PM   #20
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Smee78,

Thanks, yes your picture shows the hammer spring legs retaining the trigger pin. The trigger bosses on each side have their top half milled away so those spring legs can find the groove in the trigger pin.
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Old March 26, 2020, 07:51 PM   #21
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Quote:
The hammer spring legs do rest atop the trigger pin to prevent it walking, but there is no way the forward legs of the trigger spring will go over the hammer pin.
MY bad. You are right, and I was wrong, I had "hammer" and "trigger" springs somehow swapped in my head. The HAMMER SPRING keeps the TRIGGER PIN from walking out, not the other way around as I mis-stated it. I have removed the incorrect information.
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Old March 26, 2020, 10:15 PM   #22
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Edited my posts as well to remove further confusion... thanks for clarifying.
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Old March 27, 2020, 08:34 AM   #23
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My POF trigger came with the KNS anti-walk pins free as a package deal a couple of years ago.
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