View Full Version : walking pin
When I rapidly fire my SBR the hammer pin tries to slip out.
It is an 11.5 Barrelled AR-15, with a DPMS parts kit.
My question is has anyone tried the Knights Anti-walk pins? If so how do you like them. I have heard that they can "egg" the holes in your lower, any experience?
Is there anything else I can do to stop the pins from coming out?
Thanks in advance.
Iraqgunz
08-06-2010, 23:15
The issue is that something is either incorrectly assembled or damaged. DPMS is pretty much at the bottom of the bin so it's hard to say.
One thing you need to look for is that the "J" spring is in place. The "J" spring is located within the hammer itself. Remove the entire LPK and inspect it. The proper order is this;
1. Remove the hammer pin and hammer first.
2. Remove the trigger pin, disconnector and trigger.
When you look at the hammer there should be a spring on the bottom. If it is there then look through the hole where the pin goes. You should see part of the spring slightly protruding. If you don't then something is wrong and you will need to replace the hammer. You can replace just the "J" spring itself but it is a PITA.
If everything appears in order reassemble. You need to understand that the order is important because the legs of the hammer spring are what holds the trigger pin in place.
The "J" spring holds the hammer pin.
The pins you are referring to are called KNS anti-rotation pins. People that buy them do so because they have some fear that the pins from the hammer and trigger rotating inside the aluminum lower will cause the holes to egg out. There is ZERO proof of this. As a matter of fact the holes that I have seen that were damaged were done so by people who incorrectly disassembled their lowers repeatedly or used the improper tools. Basically KNS pins are a waste of money.
I would buy a quality hammer and trigger from Colt, LMT or Daniel defense and try that first. Another consideration is what type of lower do you have?
Some Colt lowers were made with hammer and trigger pin holes that measured .170 inches. If you install a standard LPK (they are .155) then you can experience issues as well. However since you explicitly said hammer I don't think that is the issue.
When I rapidly fire my SBR the hammer pin tries to slip out.
It is an 11.5 Barrelled AR-15, with a DPMS parts kit.
My question is has anyone tried the Knights Anti-walk pins? If so how do you like them. I have heard that they can "egg" the holes in your lower, any experience?
Is there anything else I can do to stop the pins from coming out?
Thanks in advance.
dmgedgoods
08-07-2010, 00:06
Iraqgunz hit it on the head. That section of pin that protrudes and the tension on the hammer pin itself is what holds the pin in place. Easiest bet is to just replace the hammer and spring assembly. Seeing as "mil-spec" isn't always mil-spec, you should check the pin diameter as well. This includes checking the holes themselves. It is always worth a periodic check to make sure everything is to standard.
Mack
The Reaper
08-07-2010, 12:06
I had a new LMT lose the J pin, apparently, it had not been properly staked.
They overnighted me several parts to make sure it got fixed.
Weird problem, great customer service.
TR
I took the gun to the range today just to verify that this is still a problem. Well I screwed up my original post. I thought it was the hammer pin when in fact it is the trigger pin. Apologies for my idiocy.
Thank you for the help. I am going to take the trigger apart tomorrow and reassemble. If that doesn't fix it I'll have to suck it up and buy a new lpk. Unless it makes a difference that it is the trigger pin? :confused:
dmgedgoods
08-07-2010, 20:49
Are there any other symptoms when you fire the weapon? If the weapon fires no problem, but the pin keeps coming out, check the diameter of the pin and the pin hole. Make sure you are using the right pin. Make sure your hammer spring is sitting on the pin correctly as well. The pin should be grooved where the spring sits on both sides. I have never had an issue with DPMS, but that could be the "mil-spec" issue. Best bet is to get a quality parts kit and go from there. You aren't looking at breaking the bank, and a good trigger group is worth it's weight. That's my two cents; back to work.
Mack
Iraqgunz
08-08-2010, 02:16
Make sure the legs of the hammer spring go over the trigger pin, not under. If they are and it is still an issue I would simply get a good hammer spring and replace it. I would also make sure that the hammer spring is installed correctly. I am sure that there are pics on the internet as to how it should look.
I took the gun to the range today just to verify that this is still a problem. Well I screwed up my original post. I thought it was the hammer pin when in fact it is the trigger pin. Apologies for my idiocy.
Thank you for the help. I am going to take the trigger apart tomorrow and reassemble. If that doesn't fix it I'll have to suck it up and buy a new lpk. Unless it makes a difference that it is the trigger pin? :confused:
It appears that when I installed the hammer spring I placed it backwards. The "legs" from the hammer spring came over the top. This allowed the trigger system to function correctly but it did cause several FTFs. Apparently this also wasn't keeping enough tension on the trigger pin to keep it from walking.
I removed the hammer flipped the spring and while I havn't made it to the range with it yet the pin now is locked up tight when the hammer is cocked. There is now only minimal movement when the hammer is decocked.
Thank you for all of the help. I'll report back if this still does not solve the problem but I anticipate that it is resolved.
Who'da thought it was something I did wrong :rolleyes: :lifter:D
Animal8526
09-09-2010, 21:24
As an aside here... the KNS pins aren't entirely useless...
They will remove just one slight iota of slack in the trigger pull on an otherwise slopless precision AR.
Really quite a bit less than what most people will notice though. YMMV.
Fredmisery
03-13-2011, 02:08
I have actually seen damaged pin holes on a few receivers. If the anodizing wears from the pin holes (usually hammer and sear) the aluminum is softer and the holes can get "egged out" with enough firing. This has been a problem with sear pin holes on converted AR-15's, (legally registered NFA conversions I'm talking about) and a few early manufacturers painted receivers instead of anodizing leaving the surface softer, as anodizing tends to harden the aluminum when done correctly. Granted the guns I have seen this in are all select-fire M16's and not semi-auto AR's and most have been rentals from ranges. Don't see much use for them in a semi-auto weapon, but my M16A1 is a classic and in excellent condition and I shoot the heck out of it, so I use the pins on that platform alone. Considering what the receiver is worth, I'd rather replace pins than have to install bushings in egged out holes.
My $.02
Iraqgunz
03-13-2011, 21:57
Fred,
With all due respect I'll call bullshit on your theory. I was issued an M16A1 rifle in basic that was probably used during Vietnam.
I have seen M16A1's in the military that were restamped and converted into M4's and M16A2's. How old do you think those were? Guess what? Pins were not walking loose.
So according to your theory the military should be replacing a lot of lowers because they are after all, "select fire".
KNS pins are a gimmick and they have yet to prove to be a benefit at all. Pins walk loose because the receiver is out of spec, they are assembled incorrectly or the springs are worn out.
I have actually seen damaged pin holes on a few receivers. If the anodizing wears from the pin holes (usually hammer and sear) the aluminum is softer and the holes can get "egged out" with enough firing. This has been a problem with sear pin holes on converted AR-15's, (legally registered NFA conversions I'm talking about) and a few early manufacturers painted receivers instead of anodizing leaving the surface softer, as anodizing tends to harden the aluminum when done correctly. Granted the guns I have seen this in are all select-fire M16's and not semi-auto AR's and most have been rentals from ranges. Don't see much use for them in a semi-auto weapon, but my M16A1 is a classic and in excellent condition and I shoot the heck out of it, so I use the pins on that platform alone. Considering what the receiver is worth, I'd rather replace pins than have to install bushings in egged out holes.
My $.02
I'll confirm Iraqgunz' post.
A few years back I was a lead small arms repairer at the Armor School's weapons pool.
They have many M16A2s converted from A1s that have H&R & GM Hydramatic Lowers used for the BCT companies.
These lowers were made - by my investigation - during the big build up in 1968, that's right 1968.
We were just starting to get some of these lowers to fail trigger and hammer pin hole gaging when I PCS'd. Even then, the pins didn't walk out, we got double fires on trigger release even after replacing all the fire control components.
I wouldn't hazard a guess at the number of rounds fired over 4 decades.
You don't need KNS pins, but people buy them to make themselves 'feel better'.
Would there be any reason to specifically avoid these? I ask because I recently ordered a lower parts kit that included these. I didn't know that they were part of it at the time and ordered the kit for the included grip and ambi selector.
My opinion?
They're paid for, go ahead and use them.
The damage I've seen to hammer and trigger pin holes is most usually related to people hammering the pins into place when the pins are poorly aligned and from repeated, unnecessary, disassembly of the lower receiver group.
I can imagine a blow back gun imparting additional stress to the H/T pins but not the common set-up.