AR junked firing pin retainer twice. What's the problem?

S

Silveragent

CGN Ultra frequent flyer
EE Expired
Rating - 100%
22   0   0
Location
Vancouver
Twice in a competition setting in the past few months my Norc has junked the firing pin (cotter pin). Basically in the middle of shooting the B/C would jam forward and after freeing it, discovered that somehow the firing pin retainer had come loose in the barrel. After the first incident I replaced the retainer pin and shot maybe 3-400 rounds through the Norc until first day of competition yesterday came up with the same problem, though after shooting 30 rounds.

The first time the pin was almost straightened out. This time, it showed up bent a bit but with pliers I could probably make it usable again.

What is this a symptom of? Handling? Something wearing out? Improper pin for the Norc? (This is the CQA).

When I install the cotter and the firing pin I will do that test where you snap the b/c downward to show that the firing pin is held in, so I feel like I'm installing it properly.
 
How is your bolt carrier machined? If the lower portion is machined out - the hammer can drag on the FP and deform the firing pin retaining pin.
 
The answer lies in a combination of three things.

Your bolt Carrier.

Your hammer.

Your firing pin.

Observe this image:

AR-M16-Bolts.jpg


Your bolt carrier, I suspect, is quite similar to the "SP1" carrier. Note that in the 2nd portion of the image, it is the one with the exposed firing pin due to the additional ramp cut into the bottom of the bolt carrier.

Observe this image of hammers:

1pjtb7


The far left hammer with the rounded front, and hook on the slope is an M-16 type hammer.

The center hammer has had the M-16-hook removed from the rear slope, so that it will not engage with the FA Disconnector,enabling FA fire.

The third hammer (on the right) has had the M-16 hook removed from the rear slope, AND it has a notch cut in the face.

This notch is designed to ride in that slot you see in the "SP1" style bolt.

Background point....Colt, in the 1980's and 90's made a number of changes to the internals of their AR-15's to prevent the use of M-16 parts, these included (but are not limited to) different diameter hammer pins, hooks, different bolt profiles, etc, all designed to prevent the use of M-16 parts in their AR-15 rifles. This was to make sale of the AR-15 easier, as the rifle was less compatible with military parts.

Here's a sample view of different changes made to the bolts:

AR-15%20Bolts%20Carriers%201.JPG



Here is the last piece of the puzzle, the firing pin:

2mdl4w2.jpg


Look carefully at the largest diameter section of the firing pin. You will note that one is smaller than the other.

The larger diameter firing pin is designed for an M-16 without that fancy extra ramp cut on the bottom of the bolt. In fact, you can use either firing pin in an M-16, it won't matter.

Using an M-16 firing pin, however, in a bolt with that ramp, will result in the major diameter of that ring on the firing pin protruding and obstructing the end of the ramp on the back of the bolt.

When using an M-16 firing pin, in an SP-1 style bolt, with the "notched face" hammer, it will jam, or at least, hang-up, and cause the firing pin retaining pin to be bent and damaged.

Your solutions:

1. Get a "M-16" style bolt carrier with no ramp.

or

2. Get a rounded hammer (instead of the notch) and get an AR-15 firing pin instead of an M-16 firing pin.

No in-between.

I run a rounded hammer in all my rifles.

I hope this explanation makes sense.

NS
 
Wow that's awesome information, Navy Shooter. Really great stuff. I've bookmarked this so I can diagnose it when I get home. Thanks a lot.
 
Seen it a "couple" of times over the years.

Biggest problem with people buying "mishmashed" together rifles is you get a cobbled-together parts set and stuff like this crops up.

NS
 
After that excellent explanation I hesitate to make further comments. However, I will add this in the interests of covering all the bases. I'm assuming (hoping) that you're using a proper firing pin retaining pin and not just a common cotter pin of the same size. AR-15/M16 FP retaining pins are hardened but regular cotter pins are not and can shear off or bend quite easily. It's probably not this but sometimes the little things get overlooked.
 
Thx NS - I'm utterly not conversant with the Norinco variants, so I was spitballing.

FYI new Colt carriers I have seen on commercial guns from this year have the M16 carrier again.
 
Silveragent said:
ted_dent, this was the replacement I had bought (989-015-014WB):

jyOLPsi.jpg
Click to expand...

That's the correct pin. There are the older style solid FP retaining pins that might be more resistant to shearing/deformation. I don't know if Brownells. carries them but an internet search might turn something up.

Edit - just checked. KNS Precision makes one. It's on their website.
 
Great post, NavyShooter. I just pulled my CQ-A apart and it has what looks like the AR-15 enhanced bolt in it, along with a notched hammer. If OP's is the same, he hopefully doesn't have the SP-1 problems you describe.


Mark
 
How did I learn it?

Built a few AR's.

Owned a few AR's.

Trouble-shot a lot of AR's.

Been playing with the AR Platform for over 2 decades now. I'm not an expert, I'm an RKI (reasonably knowledgeable individual) with lots of hands-on experience with these.

I suspect that since the end of the original AWB in the US, and the virtual explosion of AR-15's, parts, and new manufacturers, that the many minor changes that Colt put into their lowers have, for the most part, been discarded for the ability to use "milspec" parts.

Here is a view of the "guts" of an M-16/C-7 lower receiver to compare:

nfa-ar15rr-02.jpg


You can see the Auto sear disconnector, with the hammer (and the notch at the rear). Note also the distinctive straight walls of the milled pocket for the FCG.

Now, observe this photo:

DSC07504copy.jpg


You can see here the difference in the milling done in the lower receiver for the FCG pocket area for these two semi-auto rifles.

Colt took it one step further, you can see the block that has been inserted (with COLT stamped on it) in the area where the auto-sear would normally go. This also prevents installation of the Full Auto Bolt carrier group with the full-round part on the bottom at the rear.

Here's another variation to prevent installation of an auto sear, or Drop In Auto Sear:

DSCN1115.JPG


And a different angle of the Colt block:

standard.jpg


You can see that the "Through Pin" is located in just about exactly the right area for the Full Auto Disconnector pin hole to be drilled....so if you removed the pin, removed the block, and milled out the FCG to fit an auto-sear (width-wise) you wouldn't have enough meat left in the metal to drill the hole for it's axis pin....

Colt spent a LOT of time and money to make the AR-15 HARD to be converted to anything but semi-automatic, and these changes were why the rifle was able to live on through the bad days....it was clearly recognized by the BATF (ATF at the time) that they might LOOK the part, but most definitely were NOT capable of full auto, and had been carefully modified (hammer, bolt carrier, trigger, firing pin, safety, metal block, pin, non-standard pin sizes, milling machine required, etc) that it was able to easily be proven that due diligence and THEN SOME had been taken by Colt to ensure the rifle was damn near impossible to convert to an illegal full auto.

Many of the newer manufacturers on the market don't put in this block as seen above, the other internal changes are enough to keep multi-letter departments satisfied.

Hope this helps.

NS
 
Navy Shooter, I looked at what I have and like mmattockx, I have the "AR-15 Enhanced" bolt.

The firing pin is the one with the larger diameter on the right in your picture.

And my hammer is the third one that has the notch cut out of the face.


Here's a gallery showing the bolt and firing pin.

Jono, don't worry, I have a backup AR. I would have brought it Sunday but I hadn't properly sighted in my sight yet. It's a shorty with SPARC on it.
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom