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!

Not sure if I should post at Troubleshooting section or here, I guess Troubleshooting section is more for regular 5.56 ARs, 7.62x39 if more like an AR Variant.

In my experience, russkie ammo needs the extra power hammer spring.  Yes, it makes your trigger pull heavier, but it is what it is.

There are specialized aftermarket triggers you could add in, still retaining extra-power springs, but giving you a lighter trigger pull, if that's very important to you.

Neither of my x39 ARs require heavy hammer springs.  They both have match triggers in them with enhanced firing pins.  Zero issues with thousands of rounds of Barnaul and GT ammo thru them.

Are your enhanced firing pins PSA?
What should I look for if it is the upper? I double checked hammer spring installation. It is not backward. I heard people say headspace can cause it but round can be fired while held on AR claw extractor so headspace should not be the problem. Below is a picture of primer dimples of fired and hang-fire. This is before I bent the hammer spring back, after is a bit deeper.

I run a Black Rifle Arms 7.62x39 Piston Upper, their's come with an Enhanced Firing Pin, and I installed a CMC Single Stage Action 3.5 Lb Trigger without an Extra Power Hammer Spring with no issues.

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.

Model 1 Sales for my pins.



 

RedX Arms extended firing pin for $10 shipped fixed all of my light primer strikes in both my 7.62X39 AR's.
I use standard strength hammer springs.

I can't find any "spec" on  7.62x39 AR firing pin protrusion, but find one for M1 Garand "The firing pin should extend between 0.044" and 0.059" above the bolt face." http://www.garandgear.com/m1-garand-inspection

Also found a posting on AK measurement, 0.047"-0.060".
http://www.akfiles.com/forums//showthread.php?t=117567
Sounds like I do have room to "enhance" more.

FWIW I run three different 'enhanced' firing pins for my ARs firing Russkie ammo, A Model 1 Sales, A PSA and one from Black Rifle Arms. I've put all three side by side and measured with calipers, I don't see any difference in size or protrusion. Of the three the Model 1 is the oldest and has seen by far the most rounds. But I think right now the PSA is the cheapest at $8.

I'd replace your trigger spring with a new std. weight and see if that makes a difference. I've never had any problems with light primer strikes with commercial ammo but the last crate of Yugo M67 seems to have more FTF that other lots.  If you've bent your current trigger spring there's no way to know if it's at the correct weight.

Going to a Wolff extra power spring will absolutely fix any light primer strikes BUT it's quite a bit heavier than the GI spring. My 5.45x39 AR has to have an extra power spring to set off 7N6 but with a polished single stage GI trigger it's a heavy pull. I wouldn't go that route unless I had to.

You also didn't mention what FCG you run. One of my 7.62x39 ARs that's running thru the 'sketchy' Yugo surplus got an extra power spring added to the PSA polished FCG it started with. Reliable, but a heavy pull. I swapped in a RRA two stage trigger from another rifle, the two stage trigger & extra power spring still runs as reliable but has a much lighter trigger pull, actually difficult to tell the difference between the std & power spring.

I will try finding a new standard spring off ebay, the spring is cheap but S/H is expensive if I order from a store.
"You also didn't mention what FCG you run". LPK is standard "GI" from PSA.

Get the Wolff XP spring.  This is a fairly common issue.  Some people have luck without them. IME pretty much every fcg I've tried needs a heavy spring for 7.62x39.

Yea, I find some good deals on ebay for small parts when you factor in shipping. I'm fortunate to have a PSA in town so I can swing by for small 99 cent parts.
I've used the PSA polished FCG for two builds, one was the 5.45x39 rifle with the Wolff xtra power spring. Its a great FCG for the money. I did try an extra power spring in an ALG ACT FCG, which is their standard GI single stage. With the std. spring it's a little lighter/crisper than the PSA but with the extra power spring they feel identical to me.

I have a XP spring on the way. Will try it first. If works, I know it is not the protrusion, then I may try a standard spring, if I find one at reasonable price, to see if because I bent the spring and made it weak.

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.

Are you sure your carrier is closing 100% every time? If it failed to completely close the carrier would rob some energy from your hammer.

I might try a new action spring and see if it makes a difference.

I've got 2 of these now, 1 as a spare.  

BTW, check your hammer spring to make sure it is installed correctly.  I've seen it done wrong before and still function, just not great.

You probably right, but I sent the upper back to PSA already. Now I have it back and checked!

I sent my upper back and PSA said BCG is the problem, replaced BCG, said test fired 20 rnds and sent it back to me. Less than 10 days turn around, I'm happy with their customer service. Took it to the range this morning, this time I checked if bolt locked in battery by pushing forward assist on every round while I noticed the extractor is stiff. Indeed, 3 or 4 out of around 40 rounds fired were not fully closed. They all fired this time after pushing the forward assist. Now I need to figure out what I need to do to assure bolt closed reliably! The lower has standard recoil spring and buffer and run well on 223. Add a few drops of oil to lube the gas rings but they weren't too bad before, will also try polishing the extractor and may use a heavier buffer that I have on hand. I believe I have a H2 somewhere! Try not to buy a heavier recoil spring that may cause short stroke! Any suggestions?



----  EDIT 8/20 with update which may benefit others. ----

I put in a H2 buffer and a extra power buffer spring, also add couple drops of oil to lube the gas rings. Keep the bolt well lubed. Polish the extractor a bit. Runs well now. Ejection is good, still throw spent cases 9 ft away. 7.62x39 ARs are typically over gas. I will just make this lower a dedicated 7.62x39 lower while it now has heavy buffer, extra power hammer spring and extra power buffer spring! The trigger is not bad at all with the extra power hammer spring. Somehow, I feel the group is also tighter with the heavy buffer/spring, maybe just my imagination! Happy now!:)