HAD THE SAME PROBLEM: HAMMER SPRING "LEGS" NEED TO BE ON THE BOTTOM OF THEIR ARC....SIMPLY PUT, MY SPRING WAS UPSIDE DOWN. LEGS WERE ON TOP. SWITCHED IT, WENT TO THE DESERT THIS WEEKEND, AND NOT ONE MISFIRE!!!

I've built about 20 rifles over the years.  My last and most recent build I did over the dinner table with a few beers.  

Went shooting today to test out an old upper I had today and the damned firing pin walked out on me.  I thought, dang, I must have wore out the holes too much getting the pin in, because it was the most difficult part of the build it was so damned tight.   So I was looking into getting those walkout pins and read this post...looked into my lower and OOOOOPS.  How embarrassing.  I had the spring in backwards as well.  And to think I was going off the AR15.COM lower instructions while I was building it as well....

I think they could redo the diagram and make it idiot proof when it comes to the firing pin spring.   Or make mixing beer and building a lower illegal.

Anywhooooo, won't be buying any walkout pins soon.  Sorry to whoever makes those things.

Thank you very much. I didn't have the pin issue but I had inconsistent dimpling of primers which would result in a misfire in 2 of 5 shots. I flipped the hammer spring and voila.

Thanks for the thread. I had my hammer spring in backwards and was having a misfire on 3 out of five shots. Now it doesnt misfire and I wont make the same mistake on my second build.

Thanks for this info. I remember questioning the positioning if the spring is correct. I tested it on wolf and NEVER had a problem. Then I tried X193 and click nothing.. click... nothing... 40 rds and 9 didn't fire.  Odd. But thanks. You saved me alot of headache hopefully. We'll find out when I test er out!

Was having a ton of failure to fires on my brand new (1st time) build and I noticed my trigger pin started to come loose at one point also.  Found this thread and realized my hammer spring was installed upside down!  Hopefully that was all that was wrong!

Thanks for the sticky my new ST lower has a walking pin and ocassional mis fire. Sure enough hammer spring is backwards.

Thanks for this thread, guys!!

I've assembled 10+ lowers over the years and couldn't figure out why my new build was failing to fire and had walking pins and it was driving me nuts!!!

Sure enough! My freakin' hammer spring was backwards. Quickly switched that sucker around and like magic, problem solved.

Trouble shooting forum saves the day again.

Thanks for all the information in this thread. Went to the range yesterday with my first self-assembled rifle (PSA Stripped lower + PSA Lpak) and had these same issues. Trigger pin walking to the right 3 times and 2 light primer strikes out of about 600 rds . I dont have the rifle with me but im betting i did something wrong. Ill find out tonight! Thanks again for all the useful information, photos etc.

looks to be in backwards

my last build I also failed to pay proper attention while installing the hammer spring, I was distracted .......

as it has been stated already, if you correctly install the hammer spring your trigger pin will not walk


the first pic is a incorrect installation of the hammer spring





the second pic is a correct installation of the hammer spring

The pictures in this threas just saved another new AR build from light pin strike frustration.
Thank you all for the great pics and sharing what you know with your fellow enthusiasts!!

SI

So many say to make sure the hammer springs rest on the top of the trigger spring
but it's equally important to be sure the hammer spring legs wind out from the bottom.
not the top. If the legs come out of the top of the coil, the hammer spring is in wrong.

I kept reading the same diatribe, "look to see if the springs are resting on the top of the
trigger pin", but that was only part of the issue.

I compared the one I had that was walking out, with pictures from the web and two other lowers
that I have.  My other lowers came out the bottom, this one came out the top.

I looked at two pictures, one showed one leg from the top and the other from the bottom,
which is incorrect, from my thinking.  The other one, from Dano (picture by Eric) is the correct
way, both legs come out the bottom.

If anyone is using the TM as their guide, this will get them on the wrong path, as the burst FCG
has a hammer spring that winds the opposite.

My brand new Ilion, NY Bushmaster had a walking trigger pin right out of the box. For the life of me I could not get the hammer spring to seat in the notch on the pin good enough to hold. I used a punch and pushed the pin out, reversed it and put it back in. That fixed the problem. My guess is the hammer spring leg was tweaked on one side, so reversing the pin allowed the other leg to hold?

http://www.ar15.com/forums/t_3_66/241858_New_Trigger_and_hammer_pins_walking_out__Why_my_rifle_is_not_igniting_the_primer_.html

Nowadays part quality makes owning a micrometer mandatory.  Far too many parts are being sold that may look like a deal but the end results are nothing short of sloppy. I.E. I purchased a set of anti-walk pins advertised to be oversized at .156" diameter. When the pins arrived I checked them right away for specs and low and behold the pin diameter measured .150 inch. That's .004" under an OEM pin so two pins add up to .008" worth of slop. Needless to say the sloppy pins were back in the mail within 10 minutes and an e-mail was sent advising the seller of the problem with an ultimatum to either send pins that measure .156" or issue a refund. Well I got the refund and not one word of an apology, explanation, etc.
Unfortunately it was back to the drawing board again and searching for oversize anti-walk pins. Eventually I came across an almost identical set of pins advertised exactly like the ones I had purchased with one exception that these pins were all black and they were from JP Enterprises. It appears the seller of the slop pins I had returned must have copied JP's entire ad because the wording and specs were identical. With shipping the JP Pins were pricey but they were exactly as advertised so I'm a happy camper.
I also checked the feedback for the seller of the slop pins and they received many accolades from buyers who apparently know nothing about micrometers.
JP Enterprises Anti-Walk Pins

Went through my first tactical rifle training class yesterday and had a lot of light primer strikes and trigger pin walking out. Came here and started researching and low and behold I'm a dumbass who put his trigger spring in upside down. Thanks to this sticky and the helpful pictures I'm back up and rocking!

Thanks fellas, inspected my last two builds and had forgotten to get the hammer spring above the trigger pin. Fixed in 5 min and GTG. Love AR15.com forum.

This article helped me out a lot guys thanks!

Just got done building my ar. The first time I took it out it would not fire but a few time then the 2nd time it fired 60 out of  60 rounds and yesterday about 10 out of 100 rounds would not fire. The primer has no marks on them. the ones that fire are getting hit good with the pin. My springs are in right done checked that. It has the hipper tuch edt trigger

New AR 15 and installed Geisselle SSA trigger. Hammer Pin walked to left. Emailed them, they said ensure j hook is in. I verified via audible click and watching it move into place.
Still walks. Swapped trigger and hammer pins. Both seem identical, same thing, as Hammer pin walked after one magazine.
Please help. One pic is with pin in and one is pin walked.

Install   Anti-walking pins.

thank you

Your lower receiver may call for 0.154, 0.155, or 0.171 trigger pins especially if it's older. If you use the wrong size, the pins will be loose and walk out, and fail to ignite. I had that problem trying to use 0.154 pins in a 0.155 receiver. Either that or you installed them wrong

I'm having a similar problem on my new build with a Ruger lower using a Hiperfire Genesis Trigger. I took it to the range for the first time this weekend and the first 2 mags seemed to fire ok but then it seemed to fail to ignite the primer and of course eject properly. The range worker thought perhaps too light of a trigger but then felt it and said it must be something else. He inspected everything else and found no issues. When I got home after disassembling the lower I discovered that the hammer was striking the part of the Magazine frame and it looked as if the hammer wasn't traveling far enough. I marked the area on the hammer where it as striking the frame and disassembled it. I removed about .03" at that area thus allowing the hammer face to move forward about that much.
My question is has anyone else had this problem? What was your solution?

Regarding my hammer pins walking I plan on installing some Anti Walking pins.