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Posted: 9/27/2011 9:40:20 AM EST
How easy are these pins supposed to go in? I pushed mine in with my finger tips and I'm betting I could push them out just as easily. Is that right? Is there two different sizes of pins/holes?

I've got an aero lower & DPMS LPK.
Link Posted: 9/27/2011 9:46:38 AM EST
The LPK stacks like dominoes, one part helps hold in the next. Once completely assembled, they should all need positive pressure to
snap out.

As an example, the hammer spring legs lay over and fit into, the trigger pins recessed grooves to hold it in place.
The tension on the hammer from the hammer spring will provide enough lateral tension to hold the pin in place no problem.

But yes, there are two different sized holes, noticeably different sized. .153" is the norm I believe? Someone correct me if I am mistaken?
Link Posted: 9/27/2011 7:08:05 PM EST
I watched many lower assembly tutorials on youtube and they all seemed to need to tap the pins flush with a rubber mallet. I needed no tool whatsoever to get them flush. Does that sound normal. I'll probably end up with that KTAC? KNAC? non-rolling do-hickey but I notice that comes in two sizes.. which to get? :P

A micrometer isn't in the budget for this build.
Link Posted: 9/28/2011 3:15:49 AM EST
[Last Edit: 9/28/2011 3:45:58 AM EST by Bang-Flop]
Originally Posted By toren25333:
I watched many lower assembly tutorials on youtube and they all seemed to need to tap the pins flush with a rubber mallet. I needed no tool whatsoever to get them flush. Does that sound normal. I'll probably end up with that KTAC? KNAC? non-rolling do-hickey but I notice that comes in two sizes.. which to get? :P

A micrometer isn't in the budget for this build.
[/quote


IIRC std. pins are .154". I can push all mine in by hand except for the Giessele which again IIRC is .155
and you need to use the supplied tool to insert them. I've never had to use the KAC (or whatever they're called pins), and I've never had pins "walk on me! You shouldn't need them if you're using quality parts.

Bang-Flop

ETA: RPM 509 does a good job of describing the interlocking structure, and why you shouldn't need the KAC pins, unless you're at the edges of tolerances on the lower, and the std. pins. Also he could be correct about the dimensions of the std. pins, as I was just trying to recall from memory the size of the std. pins.

Link Posted: 9/28/2011 6:12:07 AM EST
I put my first lower together this weekend. I used the Brownell's video's Brownells AR15 Assembly Video's
In the video for installing the trigger the host of the video pushes it in with his hand, no tools needed.

The pins you are looking at are KNS pins. They come in 3 sizes and 2 different styles, so make sure you know the size of the hole on your lower and the style you want.
KNS Gen 2 Mod 2
Link Posted: 9/28/2011 6:34:39 AM EST
USGI hammers and clones have a J-spring that captures the hammer pin on the center notch.
I can’t ever recall putting in a hammer pin that did not need just a little friendly persuasion to get the pin past the center point.
The anti-rotation pin sets decrease wear on the pin holes in the lower receiver. The hammer pin in particular tends to rotate with the hammer.
Link Posted: 9/28/2011 6:37:10 AM EST
Originally Posted By PFC:
USGI hammers and clones have a J-spring that captures the hammer pin on the center notch.
I can’t ever recall putting in a hammer pin that did not need just a little friendly persuasion to get the pin past the center point.
The anti-rotation pin sets decrease wear on the pin holes in the lower receiver. The hammer pin in particular tends to rotate with the hammer.


+1

The j-spring usually necessitates rubber hammering the hammer pin.
Link Posted: 9/28/2011 12:37:16 PM EST
[Last Edit: 9/28/2011 12:38:50 PM EST by mikeyp03]
Its normal, I noticed that when I watched the videos for my first lower build too....I just took it to be that it was an old video and maybe the older lpk's were a little different, maybe they were actually roll pins for the trigger and hammer pin.....? I dunno but its normal that they go in easy, mine even walk a little on two rifles, but they will never actually walk through and fall out, so I dont see a need for those kns anti walking pins.

Edit: Just push the pins in a little with your finger whenever you notice they're not lined up perfectly with the receiver.
Link Posted: 10/1/2011 8:43:28 AM EST
AFAIK FCGs use solid pins not roll pins. Not to say there is not some exception out there.
The trigger pin should go in easy, the hammer is not hard, but one should meet resistance at the J-spring. As the J-spring is what holds the hammer pin in place very low or no resistance is bad.
I don’t know what the tolerance spec is, but if I had a pin that walked I would consider that a problem. Pin rotation is a definite factor in lower life. A pin that walks is going to create an abnormal wear pattern. YMMV
Notice than KNS describes their pin set as non-rotating not anti-walking. Also notice their hammer pin is grooved in the center so it can be captured by a J-spring.
Link Posted: 10/1/2011 5:36:38 PM EST
Good info, thank you.

I hadn't even considered things wearing unevenly. The nice thing about loose pins is they're easy to change. :) The DPMS trigger in here is heavy but breaks really fast and clean.. I'm gonna figure out if I want to keep this trigger or not, then I'm definitely gonna go with the KNS pins. At that point I'll have to figure out which size pins I need.

BTW.. you can't just buy a 3-4lb spring set can you?
Link Posted: 10/2/2011 9:43:34 AM EST
Burnish in a good coat of moly on the trigger and hammer’s sear surfaces.
Use a set of Tubb’s NM CS hammer and trigger springs.
I have never personally used a lighter spring set than Tubb's because I do not want to compromise reliability with hard primers.
Link Posted: 10/2/2011 12:18:17 PM EST
There's 3 springs in FCG.. can't you get a lighter trigger spring to reduce pull weight but still keep a strong hammer spring to ensure primer ignition?
Link Posted: 10/2/2011 8:20:11 PM EST
Actually there are four springs. What I have already posted is about as far as I will go with a standard FCG.
There is a sticky on this forum on FCG mods.
A quick web search will come up with any number of ways to mod a standard FCG.
If you really want a better trigger, any Geissele FCG will be way better, not just a little better.
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