PSA 7.62x39 AR47 light primer strikes

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HankC1

New member
My PSA 7.62x39 AR47 has light primer strikes 1 out of 4 rounds. The ammo is Russian Barnaul white box. At first I thought the firing pin is not a 7.62x39 firing pin and PSA sent me another 7.62x39 firing pin (P/N 505873), appears to be the same as what I have already, same length same firing pin protrusion. Pull my 5.56 AR, the 7.62x39 firing pins indeed have longer tips and protrude longer compare to 5.56 firing pin. Originally, I had hammer spring bent a bit to reduce trigger pull weight like all my other ARs, now having light primer strikes, I bent it back, still about the same % of mis-fires but a bit deeper strike marks, originally was more like a nick, now I can see a tiny dimple! On the fired rounds, the primer dimples look normal, pretty much have the protrusion printed on the primers.

Do I need extra power hammer spring or something wrong with the upper? Is PSA 7.62x39 firing pin (P/N 505873) indeed the "enhanced" firing pin that everyone talk about or I still need to "enhance" the pin by removing more material off the firing pin stop.

It is hard to take an accurate measurement on the protrusion, my caliper shows it is 0.046" by taking a 2-step measure as protrusion = depth to bolt face (0.124") - depth to firing pin tip (0.078"). 0.046" is plenty to me!

I don't know if Barnaul 7.62x39 is known for hard primers, my AK and VZ2008 and my mauser home built 7.62x39 bolt gun all shoot fine and like it. I don't have Tula or Wolf to try. I heard Tula and Wolf have hard primers, so I don't really need to bother with them!
 
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HankC1

New member
Can someone tell me what is the protrusion needed in 7.62x39 AR, what protrusion you have? I did a google search, and find one post says .050" required, but I don't know the credential of the poster. I just pulled one of my RPKs and the protrusion looks longer, measure it, has .055" (.113" to bolt face -.0585" to firing pin tip). AK/RPKs have loose tolerance, I can imaging they need more protrusion, what is required in 7.62x39 AR! I took measurement on the 3 hang-fire ammo. The primer depths are 0.010", 0.011", 0.0115". Check my PSA protrusion again with a better method, clearance between firing pin stop to the back of bolt with feeler gauge, and I have .040" GO/0.041" NO-GO.
GEDC0089_zpsg7gder6k.jpg
 
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turtlehead

New member
I think you may have weakened your spring by fussing with it. Do you have a spare in your parts box to try?

People have been reporting good results with the enhanced firing pin and you've tried two. Maybe it's not the pin?
 
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Mobuck

Moderator
"I think you may have weakened your spring by fu{ss}ing with it."

Replace the spring with a new standard spring and see if the problem is resolved. If not, swap in an "extra power" hammer spring.

I've been chasing a problem with my 5.45 related to first round(manual cycling the bolt)light hits and ended up changing to the extra power spring. It didn't solve the problem 100% in very cold weather and I later determined part of the cause was due to crud build up in the bolt lug recesses. The bolt wasn't fully rotating to the locked position when hand cycled. Even though I pulled it fully to the rear and released there was enough drag from a slightly kinked charge handle that it slowed the bolt enough to effect the lockup. Keep in mind this carbine had spent 4 months outside subjected to dust, occasional rain, and during winter some blowing snow so it was due for a thorough cleaning.
Moral of the story: lots of things can cause what appears to be a simple light FP strike.
 
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Tomas

New member
Make sure you didn't install the hammer spring up-side down. I don't mean to imply anything about your intelligence...but the FCG will function with it put in this way, and will fire as well, with lots of light strikes mixed in.

Check it, and at least you can rule it out.

Tom
 
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HankC1

New member
I think you may have weakened your spring by fussing with it. Do you have a spare in your parts box to try?
Click to expand...
That is possible, but when I pull the spring out, it is straight. I don't have a spare spring to try it out, all my lowers have the spring bent (1 leg only) to reduce trigger pull weight. I probably should check out ebay to order a new standard spring. The spring is cheap, but S/H kills it.

Make sure you didn't install the hammer spring up-side down.
Click to expand...
That was the first thing I checked, not backwards.
 
9

95Blitz

New member
I had to take the bolt out and grind the back face down a little. Maybe .05 or so that will let the firing pin stick out a little more.
 
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orionengnr

New member
Looking forward to the resolution.
I have a PSA x39 AR. The modest number of rounds I have put through it so far have been trouble-free, but knowledge is power...
 
H

HankC1

New member
Put the extra power hammer spring in and took it to the range again. Now it is 1/20 hang fire! Primer hit is a little harder but obviously not enough. Picture below from left to right are PSA enhanced firing pin/regular AR hammer spring, PSA enhanced firing pin/Wolff extra power hammer spring and third is a fired case. I could file down the firing pin stop or the bolt butt a little to give more firing pin extrusion, currently it is .040", I can use more protrusion, but that may void the PSA warranty. The upper shoots well, if fired, I like to keep it but I want a reliable rifle. I also notice the headspace is generous, spent case from this upper would not fit in the chamber of my 7.62x39 bolt gun and not even my AES10B RPK. I may just send the upper back for an exchange under PSA Life Time Warranty.
GEDC0094_zpsx6lgwgof.jpg
 
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marine6680

New member
Isn't there a slightly longer firing pin to help with this? Are you using one?

If so, I can't say modifications to the bolt will help.
 
H

HankC1

New member
The PSA 7.62x39 firing pin is "enhanced" with longer tip. I will ask PSA to take it back under their Life Time Warranty. The upper is actually bought a year ago, but I set it side until now. It has Life Time Warranty! I don't want to mess with the protrusion and risk pierced primer while there is warranty. Now I think maybe the chamber is too loose, the spent case would not even fit in my AES-10B RPK and close the bolt.
 
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Jimro

New member
7.62x39 requires a more firing pin protrusion for reliability. COMBLOC primers were designed to need more of a hit on purpose. An AK-47 specifies 0.055" to 0.060" of firing pin protrusion to be in spec, or between 1.40 mm and 1.52mm for metric fans.

There are two ways to get more firing pin protrusion in an AR, either use a normal milspec length firing pin and machine away a bit of the back end of the bolt or use a longer 7.62x39 spec firing pin. Just don't do both.

If PSA will replace your firing pin with one that is 0.009" to 0.014" longer, that would be the best option I think.

Jimro
 
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tangolima

New member
Here are rules of thumb for rifle firing pin protrusion.

1. Min. 0.04"
2. Max. Firing pin diameter - 0.01"

This is assuming little or no head clearance (no excessive headspace). How does your rifle headspace? I don't know the details, but one the measurements of firing pin protrusion in your previous post was referring to no-go gauge. Does it mean the action closes on no-go gauge with extra clearance? Excessive headspace causes misfires as it undercuts the firing pin protrusion.

How did you make the firing protrude during your measurements? Was the pin head flush with the back of the bolt, or you pushed it below flush until it stopped?

-TL
 
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