AR15.Com Archives
 Trigger and hammer pin's spinning
98hd  [Member]
3/8/2006 2:32:32 PM
I've searched and cannot find a fix for this. The trigger pin and hammer pin both spin w/ the respective part. They are not walking out, just spinning in the reciever w/ the movement of the hammer/trigger. So what / how do I fix it?
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FALARAK  [Team Member]
3/8/2006 2:37:52 PM
Buy a set of KNS anti-rotation pins.
mr_wilson  [Team Member]
3/8/2006 2:39:12 PM
Well , given the fact my eyes are generally on the scope, Aimpoint red-dot or front sight post, I have never in my life actually noticed, whether this occurs on any of the my AR15s I have owned over the decades.

How in the heck would one know this was happening in the first place?

As long as my pins ain't walkin, I could care less, YMMV.

Mike
98hd  [Member]
3/8/2006 2:52:57 PM

Originally Posted By mr_wilson:
Well , given the fact my eyes are generally on the scope, Aimpoint red-dot or front sight post, I have never in my life actually noticed, whether this occurs on any of the my AR15s I have owned over the decades.

How in the heck would one know this was happening in the first place?

As long as my pins ain't walkin, I could care less, YMMV.

Mike



Well I had read something about it after discovering this forum. So today I took off the upper and released the hammer. My pins are slightly scarred from being taken out previously. I moved the hammer back and forth and the trigger, and could notice the marks on the pins moving w/ the hammer and trigger. So that is how I noticed.

Those KNS pins look like a good idea, however having those connecting pieces on the outside of the reciever is far less than attractive.
FALARAK  [Team Member]
3/8/2006 3:13:23 PM

Originally Posted By 98hd:
Well I had read something about it after discovering this forum. So today I took off the upper and released the hammer. My pins are slightly scarred from being taken out previously. I moved the hammer back and forth and the trigger, and could notice the marks on the pins moving w/ the hammer and trigger. So that is how I noticed.

Those KNS pins look like a good idea, however having those connecting pieces on the outside of the reciever is far less than attractive.



It will grow on you. Most M16 owners use them to keep their holes from wearing out.... so you can pretend your toy has NFA cool factor.
98hd  [Member]
3/8/2006 3:25:36 PM

Originally Posted By FALARAK:


It will grow on you. Most M16 owners use them to keep their holes from wearing out.... so you can pretend your toy has NFA cool factor.



I suppose it's better than letting the pins wear in a perfectly good lower.
metroplex  [Team Member]
3/8/2006 7:37:14 PM
Are the KNS anti-rotation pins really necessary? I plan to shoot a lot through my lowers. I just don't want it to wear out to the point the pins walk out and turn the rifle into a $800+ club.
Teknic  [Dealer]
3/8/2006 8:32:45 PM

Originally Posted By metroplex:
Are the KNS anti-rotation pins really necessary? I plan to shoot a lot through my lowers. I just don't want it to wear out to the point the pins walk out and turn the rifle into a $800+ club.



It's not needed but define Need?
Dano523  [Moderator]
3/9/2006 1:03:11 AM
With the spring tension of the hammer J spring and the hammer spring legs against the pins, the surface tension of the pins against the FCG prats themselves is greater than the receiver hole tensions, and the pins will spin.

Now regarding the Tm's, pulling the FCG is not advised by the common shooter/solder, but you have to remember that one of the specification for the ammo to be used is that the primers are to be staked in to the cases to prevent them from being lost/blown into the receiver cavity/action. Translating this to civilian ammo and shooters, it is not uncommon to have a blown primer every blue moon that makes it way under the trigger and disables the rifle. Since the standard FCG with standard pins can be disassembled with nothing more than a bullet tip and stick if needed, the slight wear to the receiver caused by the pins rotating outweighs a tool needing to be used pull the FCG (read if you do have the allen wrench when it does happen). Also, since USGI receivers are still in service after hundred of thousands of rounds using/with the standard pins rotating, worrying about pin wear on a properly lubed/maintained rifle is way over the top.


Now since KNS pins have been bought up, you really need to keep in mind that nature of the beast.

Te real rifle that benefits from the KNS pins is the 9mm (blow back type units). On these units, the hammer tension against the non-ramped bolt (carrier since it’s all one part) is part of the equation of the mass that holds the bolt forward against the barrel during the blow back action of the system. Do to this non ramped edge to smooth out the hammers transition movement, the 9mm unit hammers can do a number of the hammer pin, and even oblong the receiver hole in a very short time.

The pins themselves on the KNS unit are not stronger than standard FCG pins, but if the hammer pin does snap, it is at least retained in a semi normal position and the rifle will continue to the rifle. Also, since the two pins are linked together, these helps to reduce the obliging of the receiver’s hammer pinholes since the pressure of the hammer to the pin is transferred to both pins.

The draw back to the KNS pin system, even in the blow back units, is that there will be more wear from the FCG to the pin it’s self since the pins do not rotate with the FCG. And as stated above, if the FCG needs to be pulled (such as a blow primer, or mantiance), a allen wrench is needed to pull the pins.

If you feel that the increase longevity of the 223/5.56 Nato lower receiver to be passed on to future generations (read being able to take the lower past the 300,000 round mark), out weights the need to ready available pull the FCG (pins) without special tools, then by all means, buy the KNS set for the rifle.
GFrancis  [Member]
3/10/2006 9:17:54 AM

What a coincidence!

I was going to ask this very same question yesterday.
Dano523 has a very good answer to this question. Thanks!

A possible solution that had occured to me was the use of pins that
are .155 in diameter rather than the standard .154.
These pins are available from Brownells or from Rock River Arms.
RRA refers to them as NM (National Match) hammer pins.

I wasn't sure if they would provide enough friction in a receiver
hole that has been somewhat worn.

A different possibility is to buy some ,174 pins and chuck them up
in a drill in order to "sand" them down to the exact size to fit snugly
into the receiver pin hole.
The newly sized pins would need to have the middle groove reground
as well. This would be a bit of work but not all that tough to do.

Any more thoughts on this?
98hd  [Member]
3/10/2006 12:36:30 PM

Originally Posted By GFrancis:
What a coincidence!

I was going to ask this very same question yesterday.
Dano523 has a very good answer to this question. Thanks!

A possible solution that had occured to me was the use of pins that
are .155 in diameter rather than the standard .154.
These pins are available from Brownells or from Rock River Arms.
RRA refers to them as NM (National Match) hammer pins.

I wasn't sure if they would provide enough friction in a receiver
hole that has been somewhat worn.

A different possibility is to buy some ,174 pins and chuck them up
in a drill in order to "sand" them down to the exact size to fit snugly
into the receiver pin hole.
The newly sized pins would need to have the middle groove reground
as well. This would be a bit of work but not all that tough to do.

Any more thoughts on this?



I had thought of the same thing, only probelm for me is I have the larger pins, I was looking at the KNS setup on brownells, and they had .155 pin kits (w/o the anti rotation setup) and a reamer available. Might want to look into that.
Dano523  [Moderator]
3/10/2006 2:30:59 PM
You lost me on the question,
Why is the FCG pins spinning in the receiver holes a "bad" thing again?

With the micro-hardness of anodizing partially equating to a Rockwell of 60 to 65, we are concerned about accelerated wear to the receiver holes when the pins are covered in parkerizing (no where as hard as the anodizing) and the pins correctly lube because? To me, I see galling from the two like metals of the pins/FCG components more of an issue is the pins did not spin.

As for the sole purpose of the just tightening up the FCG parts themselves by having the pin tight in the receiver, The tolerances of the pins to the FCG channels is in the .005 Plus range on standard parts anyway, so what is another .001 to .002 in the mix with the pins spinning

Don’t know about the rest of you, but on a service gas gun that is going to foul the parts (FCG/action) with gunpowder/brass flake fouling, getting the working tolerances too tight is going to be counter productive in the reliability of the weapon as a whole. Granted that I’m not saying that the rifle/parts has to be loose as an AK’s, but you get the parts as tight as a Swiss watch, and your going to own a jam-o-matic.


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