M&P 15 Sport fires with the safety on


April 21, 2013, 10:42 PM
Like the title says my almost new S&W M&P 15 Sport fires with the safety on. There's no difference in the trigger with the safety on or off. Is there a simple fix I can address or does this rifle have to go back to S&W?

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April 21, 2013, 10:57 PM
You have a big problem.

Broken selector?
Improper FCG assembly?

Can we see pics?

April 21, 2013, 11:15 PM
Does the actual safety lever seem to function properly? Did you replace the grip recently?

April 22, 2013, 02:02 PM
The safety lever clicks back and forth very positively it just doesn't prevent the gun from firing. I haven't taken this rifle down yet. I'm new to the platform and I'm going to have to take some time to understand how it all goes together. I haven't modified it in anyway and it has less than 300 rounds through it. When I first started shooting it I han an instance where pulling the trigger did not release the firing pin. I oiled the bolt and worked the charging handle a few times and it worked fine after that. Except for the safety.

April 22, 2013, 02:25 PM
I'd call Smith & Wesson immediately. Something is wrong.

Sent from my SGH-T999 using Tapatalk 2

April 22, 2013, 02:33 PM

so when you pivot the upper off by pushing the rear takedown pin in, you should be able to see the selector lever (the safety switch) which looks like this


it works simply by blocking the trigger when rotated over. you can see that rotated vertically, it would allow the trigger bar underneath it to be raised up higher (i.e. fired) and when rotated horizontally, it prevents you from pulling the trigger far enough.

peek in there and see if it appears to be doing that.

i can't comprehend how someone could screw that up, so i suppose the more likely issue is that the sear engagement is so short that you only have to move the trigger a tiny distance to fire it. is that the case?

the likely cause is one of the pins drilled in the wrong location, or the hammer or trigger is very out of spec.

April 22, 2013, 04:37 PM
The trigger pull seems normal. Sort of like an AK without the slap. Thanks for the input and the image. That helps a lot. I'll have to take it down and check it out. It probably has a trip to S&W in it's future.

April 22, 2013, 11:09 PM
Fixed it. The pin that retains the hammer had walked out of the right side of the lower (or the factory never installed it correctly to begin with, I'm not sure). I put it back in place and the safety does what it's supposed to. As I said, I'm new to the platform, and I'm not sure how the unsecured hammer negated the safety. So now I have a different concern. If the pin walked from the relatively few rounds I fired, it's clearly a little too loose in the lower. Is there a way to secure the pin? Thanks for all the replies.

April 22, 2013, 11:21 PM
All the pins are secured in place by the proper placement of the spring arms fitting in the groves in the pins.

Either the hammer pin was installed backwards?
Or the hammer spring was installed without one of the arms in the pin grove.

See this:


April 22, 2013, 11:26 PM
Chec you hammer for a little "J" spring. It is supposed to lock the hammer pin into the receiver via the groove in the center of the pin. And check your pin for a groove in the center.

April 25, 2013, 09:54 PM
So I removed the hammer, and sure enough, no J-spring was installed in the hammer. I've emailed Smith but haven't heard back from them. Would one of the anti-walk hammer pins also be a way to fix this problem? Are all AR lowers drilled for the same diameter pins?

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