Bump Fire / Trigger / KNS Pin help

[motopg]

I would like to set up the Bump fire rig in my M&P15-22.

Should I use the Timney 3lb 667S drop in assembly in my M&P1522? - if I can, what is the correct KNS locking pin set?

Is the KNS M&P15-22 pin set no longer necessary?
(Because my S&W stock hammer and trigger are not being used?)

Is the KNS pin set for the small pin Timney Trigger now the correct part because of the new drop in trigger assembly?

any insight / past experience anyone has with this would be greatly appreciated.
Thanks
MotoPG

 

[04jeeper]

You can get the 15-22 kns pins from primary arms. Or you used to be able to.

 

[gr8jab]

There is only one size of KNS pins for the 15-22. They must be specifically for the 15-22. They do come in multiple colors. The 15-22 receiver has thicker walls than the standard AR, and requires slightly longer pins.

The Timney trigger has a downward extending set screw that pushes the trigger assembly upward and locking the stock pins in place. However, with the 15-22 polymer lower, the set screw tends to deform and damage the lower. There are two solutions.

1) insert a small metal shim in the bottom of the receiver where the set screw impacts. I used a piece of a feeler gauge, cut with snips.

2) use KNS pins, and do not tighten the set screw.

 

[motopg]

Thank You
Perfect info! - Now I understand.....
Best Regards,
MotoPG

 

[Dikinalaska]

There is only one size of KNS pins for the 15-22. They must be specifically for the 15-22. They do come in multiple colors. The 15-22 receiver has thicker walls than the standard AR, and requires slightly longer pins.

The Timney trigger has a downward extending set screw that pushes the trigger assembly upward and locking the stock pins in place. However, with the 15-22 polymer lower, the set screw tends to deform and damage the lower. There are two solutions.

1) insert a small metal shim in the bottom of the receiver where the set screw impacts. I used a piece of a feeler gauge, cut with snips.

2) use KNS pins, and do not tighten the set screw.

What he said for the most part. Personally, I would suggest the pins. The set screws are hard to get to with the spring legs in the way, and you have to deal with shims and securing or glueing them in. Well I honestly went with pins out of ignorance of the shims needed and almost muffed up my lower pretty bad.
But I keep hearing that you HAVE to have the special KNS anti-walks for the 15-22. When I went in and got mine from a friend at my LGS, he grabbed it out of a JP kit he had. I asked about the "special" 15-22 pins and he said "nah, these work fine, you just don't catch as many threads" while I know everyone can be mistaken, I trust him with everything else so I dunno. Either way after about 1k rounds since the pins, and most of them coming through slidefire, they haven't loosened yet.

 

[Dikinalaska]

I would like to set up the Bump fire rig in my M&P15-22.

Should I use the Timney 3lb 667S drop in assembly in my M&P1522?

Also yes, it may not be the most cost effective, but it sure does work great. Especially for this intended purpose.

 

[MNBud]

I'm a little confused, it is apparent that the set screw in the Timney trigger is designed to keep the trigger mechanism from moving up or down, (from the picture with the protruding bump)so what do the KNS pins do that the stock pins cannot do?

 

[telero]

I'm a little confused, it is apparent that the set screw in the Timney trigger is designed to keep the trigger mechanism from moving up or down, (from the picture with the protruding bump)so what do the KNS pins do that the stock pins cannot do?

I was confused about this as well at first. What the set screws are designed to do is push on the bottom of the receiver, raising the trigger assembly up, which puts friction on the standard trigger pins to keep them in place. What the Timney trigger doesn't have is any way to capture the standard pins like a regular trigger group would (spring legs and the little piece of metal in the hammer) by resting in the groove in the pins. So for the Timney in a polymer receiver the set screw will deform the receiver without a shim, or you can use anti-walk pins that are captured on the ends rather than by the internal springs. With anti-walk pins you wouldn't need to use the set screw in the Timney at all.

 

[MNBud]

I was confused about this as well at first. What the set screws are designed to do is push on the bottom of the receiver, raising the trigger assembly up, which puts friction on the standard trigger pins to keep them in place. What the Timney trigger doesn't have is any way to capture the standard pins like a regular trigger group would (spring legs and the little piece of metal in the hammer) by resting in the groove in the pins. So for the Timney in a polymer receiver the set screw will deform the receiver without a shim, or you can use anti-walk pins that are captured on the ends rather than by the internal springs. With anti-walk pins you wouldn't need to use the set screw in the Timney at all.

Thanks for the reply, that clears up everything for now.

 

[Dikinalaska]

I was confused about this as well at first. What the set screws are designed to do is push on the bottom of the receiver, raising the trigger assembly up, which puts friction on the standard trigger pins to keep them in place. What the Timney trigger doesn't have is any way to capture the standard pins like a regular trigger group would (spring legs and the little piece of metal in the hammer) by resting in the groove in the pins. So for the Timney in a polymer receiver the set screw will deform the receiver without a shim, or you can use anti-walk pins that are captured on the ends rather than by the internal springs. With anti-walk pins you wouldn't need to use the set screw in the Timney at all.

Yes it's as telero put it. The set screws just put pressure on the standard pins. After I let off on the set screws until there was no more deformation, I went to the range and as I shot the trigger pins would walk out because as again telero stated, there's no spring legs to set in the recesses. You don't have this problem on aluminum lowers obviously