First shots out of M&P, good but had "triggerpin walk" [Archive]

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hamlinem

01-22-12, 15:46

Freeeeeezing at the range yesterday but got to fire off a few mags. First time out for my new M&P-15. She got great at 25, 50, and 100 yards. I did, however, have to, twice, reset my trigger pin. It would walk out from the right side and be sticking out the left.

Besides getting new pins with threaded ends and small screws, do any of you guys have any good tips and tricks for getting trigger pins to stay in place? Thanks all

C4IGrant

01-22-12, 15:48

jet66

01-22-12, 16:09

And make sure the hammer spring wasn't put in upside down/backwards. I don't know what the chances are of that happening from the factory, but mistakes happen. This pic at Brownells (http://www.brownells.com/userdocs/skus/p_080000070_1.jpg) is a nice cut-away. If it is upside down, that lower leg of the spring will be coming down from the top of the hammer pin. It doesn't sit right in the trigger pin's groove at that angle, and the pin will walk. (Did it once myself...)

Robb Jensen

01-22-12, 16:21

Before you do any of that, make sure the legs of the hammer spring are sitting ON TOP of the trigger pin.

C4

Yep I've seen one or both hammer spring legs not sitting on trigger pin before and/or the hammer spring installed backwards on factory rifles and on home 'builds'. One time on a Century Arms AR the factory had used a M16A2 hammer spring, on a 3 round burst hammer spring one side has a loop which is larger than the other (on the 3round burst cam side) and doesn't provide enough tension on the trigger pin when used on a full-auto or semi auto trigger set up and it will allow the trigger pin to walk.

hamlinem

01-22-12, 17:46

it appears from the diagram that my hammer spring is backwards. instead of coiling counter clockwise then shooting out from below the hammer pin, it coils clockwise then lays over the hammerpin and then sits on the trigger pin. thanks guys. now to dive into dissmantling the lower... yikes, i'm a lower virgin.

hamlinem

01-22-12, 18:31

flipped it around.... awesome... thanks guys.... there is much more tension on the hammer and that would explain the amount of misfires i had, hopefully. More tension on the hammer, more of a strike on the firing pin, harder hits on the primer...

I am not a gunsmith so this is my reasoning.

mpom

01-22-12, 19:17

Realize the m&p was new to you, but was it also brand new, as just out of the box? Amazing that it was assembled incorrectly. Wonder what else is wrong, and how many others escaped...

Mark

Suwannee Tim

01-22-12, 19:49

......there is much more tension on the hammer and that would explain the amount of misfires i had.....

I reckon. You should not have misfires. Not even one.

......Amazing that it was assembled incorrectly......

I removed the rear brake drums of my Mother's Mercury to inspect the shoes........ automotive brakes are some of the most highly engineered devices on the Earth and part of the plan is they cannot be assembled incorrectly. Well, not by an ordinary human anyway. The autoworker who built these figured out another way which he applied to one side of my Mom's brakes. Never underestimate the power of stupidity.

dmaxfireman

01-22-12, 19:55

I had a brand new from the factory Stag walk the trigger pin out. Long story short the pin broke and the the hammer would not catch and went burst / fa on me.

I was very popular guy for a very short period of time at the range that day. After clearing the rifle I brought it to my tailgate and found the hammer spring legs under the trigger pin.

ucrt

01-22-12, 21:12

...
...
...... automotive brakes are some of the most highly engineered devices on the Earth and part of the plan is they cannot be assembled incorrectly.
... Never underestimate the power of stupidity.

==========================================

Everytime someone comes out with something "fool proof"...
...we just come up with a better fool...

.

Robb Jensen

01-22-12, 21:17

Now you see why I disassemble and reassemble my own own ARs regardless of who manufactured it and originally built it. Murphy is an evil MFer.

Eric

01-23-12, 00:22

there is much more tension on the hammer and that would explain the amount of misfires i had, hopefully. More tension on the hammer, more of a strike on the firing pin, harder hits on the primer... You are indeed correct.

Iraqgunz

01-23-12, 01:07

OP,

I suggest that although the problem is solved, you contact S&W and advise them of the issue. Then give them the serial number and other pertinent info so that they may address the problem.

There could possibly be other AR owners out there in the same boat.