PSA 7.62x39 AR47 light primer strikes

HankC1 · July 23, 2016, 11:45 PM

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!

turtlehead · July 23, 2016, 11:49 PM

Weird. I've used Tula, Wolf and Red Army in mine with no issues.

turtlehead · July 23, 2016, 11:50 PM

Reread your post. Replace the spring with an unaltered one.

HankC1 · July 24, 2016, 06:57 AM

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.

HankC1 · July 24, 2016, 09:39 PM

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.

turtlehead · July 24, 2016, 10:24 PM

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?

stolivar · July 24, 2016, 11:55 PM

And it will eat anything

Mobuck · July 25, 2016, 06:43 AM

"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.

Tomas · July 25, 2016, 12:56 PM

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

HankC1 · July 25, 2016, 04:28 PM

Quote:

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

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.

Quote:

Make sure you didn't install the hammer spring up-side down.

That was the first thing I checked, not backwards.

turtlehead · July 25, 2016, 04:46 PM

Any good gun store should have that spring.

95Blitz · July 25, 2016, 05:16 PM

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.

turtlehead · July 25, 2016, 05:52 PM

These firing pins do not have that issue.

orionengnr · July 25, 2016, 07:33 PM

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...

HankC1 · July 31, 2016, 08:36 PM

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.

marine6680 · July 31, 2016, 09:30 PM

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.

HankC1 · July 31, 2016, 09:43 PM

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.

turtlehead · July 31, 2016, 11:06 PM

Did you try any other ammo?

Jimro · August 1, 2016, 02:47 AM

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

tangolima · August 1, 2016, 04:18 AM

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

Mobuck · August 1, 2016, 06:57 AM

" I could file down the firing pin stop or the bolt butt a little to give more firing pin extrusion, currently it is .040","

If the FP is traveling far enough to fire most of the primers, I doubt extrusion is the problem. More likely it's how hard the FP hits rather than far far it sticks out. Be advised that indiscriminate machining/filing to increase FP projection may cause primer perforation on domestic ammo.

HankC1 · August 13, 2016, 11:37 AM

An update. 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 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?

tahunua001 · August 13, 2016, 12:13 PM

I can think of two possible reasons,

or your guns not headspaced properly and your bolt face isn't making solid contact with the case head.

junk ammo, did I read correctly that you suffer from 1/20 HANGFIRES? that is not a gun problem that's an ammo problem.

surg_res · August 13, 2016, 12:54 PM

Short stroke from inconsistent gas delivery? Not familiar with Barnaul's propellant but may burn too fast/slow for the AR platform--for which this ammo is likely not tested or designed by the mfg. If you can manually cycle each round and fire without problem, then its a cycling issue. Back to the ammo again.

marine6680 · August 13, 2016, 12:58 PM

Sometimes an AR can be a little tight at first. With a new BCG this may be the case.

If after 100rds, it does not clear up and run smoother, double check for binding and other issues like headspace, as it may be on the tight side.

July 23, 2016, 11:45 PM	#1
HankC1 Senior Member Join Date: April 4, 2005 Location: Ohio Posts: 531	PSA 7.62x39 AR47 light primer strikes 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!

July 24, 2016, 06:57 AM	#4
HankC1 Senior Member Join Date: April 4, 2005 Location: Ohio Posts: 531	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. Last edited by HankC1; July 24, 2016 at 08:46 AM.

July 24, 2016, 11:55 PM	#7
stolivar Senior Member Join Date: September 24, 2004 Posts: 394	I have And it will eat anything

August 1, 2016, 02:47 AM	#19
Jimro Senior Member Join Date: October 18, 2006 Posts: 7,097	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 __________________ Machine guns are awesome until you have to carry one.

August 13, 2016, 11:37 AM	#22
HankC1 Senior Member Join Date: April 4, 2005 Location: Ohio Posts: 531	An update. 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 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? Last edited by HankC1; August 13, 2016 at 11:42 AM.

July 23, 2016, 11:49 PM	#2
turtlehead Senior Member Join Date: October 20, 2015 Location: Phoenix, AZ Posts: 1,203	Weird. I've used Tula, Wolf and Red Army in mine with no issues.

July 23, 2016, 11:50 PM	#3
turtlehead Senior Member Join Date: October 20, 2015 Location: Phoenix, AZ Posts: 1,203	Reread your post. Replace the spring with an unaltered one.

July 24, 2016, 09:39 PM	#5
HankC1 Senior Member Join Date: April 4, 2005 Location: Ohio Posts: 531	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.

July 24, 2016, 10:24 PM	#6
turtlehead Senior Member Join Date: October 20, 2015 Location: Phoenix, AZ Posts: 1,203	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?

July 25, 2016, 06:43 AM	#8
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	"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.

July 25, 2016, 12:56 PM	#9
Tomas Senior Member Join Date: May 9, 1999 Location: Blue State Posts: 441	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

July 25, 2016, 04:46 PM	#11
turtlehead Senior Member Join Date: October 20, 2015 Location: Phoenix, AZ Posts: 1,203	Any good gun store should have that spring.

July 25, 2016, 05:16 PM	#12
95Blitz Junior Member Join Date: December 31, 2013 Posts: 10	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.

July 25, 2016, 05:52 PM	#13
turtlehead Senior Member Join Date: October 20, 2015 Location: Phoenix, AZ Posts: 1,203	These firing pins do not have that issue.

July 25, 2016, 07:33 PM	#14
orionengnr Senior Member Join Date: July 9, 2004 Posts: 5,177	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...

July 31, 2016, 08:36 PM	#15
HankC1 Senior Member Join Date: April 4, 2005 Location: Ohio Posts: 531	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.

July 31, 2016, 09:30 PM	#16
marine6680 Senior Member Join Date: July 24, 2012 Location: Parker, CO Posts: 4,594	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.

July 31, 2016, 09:43 PM	#17
HankC1 Senior Member Join Date: April 4, 2005 Location: Ohio Posts: 531	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.

July 31, 2016, 11:06 PM	#18
turtlehead Senior Member Join Date: October 20, 2015 Location: Phoenix, AZ Posts: 1,203	Did you try any other ammo?

August 1, 2016, 04:18 AM	#20
tangolima Senior Member Join Date: September 28, 2013 Posts: 3,827	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

August 1, 2016, 06:57 AM	#21
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	" I could file down the firing pin stop or the bolt butt a little to give more firing pin extrusion, currently it is .040"," If the FP is traveling far enough to fire most of the primers, I doubt extrusion is the problem. More likely it's how hard the FP hits rather than far far it sticks out. Be advised that indiscriminate machining/filing to increase FP projection may cause primer perforation on domestic ammo.

August 13, 2016, 12:13 PM	#23
tahunua001 Senior Member Join Date: July 21, 2011 Location: Idaho Posts: 7,839	I can think of two possible reasons, or your guns not headspaced properly and your bolt face isn't making solid contact with the case head. junk ammo, did I read correctly that you suffer from 1/20 HANGFIRES? that is not a gun problem that's an ammo problem. __________________ ignore my complete lack of capitalization. I still have no problem correcting your grammar. I never said half the stuff people said I did-Albert Einstein You can't believe everything you read on the internet-Benjamin Franklin

August 13, 2016, 12:54 PM	#24
surg_res Senior Member Join Date: September 29, 2005 Location: Texas, 5th GEN! Posts: 621	Short stroke from inconsistent gas delivery? Not familiar with Barnaul's propellant but may burn too fast/slow for the AR platform--for which this ammo is likely not tested or designed by the mfg. If you can manually cycle each round and fire without problem, then its a cycling issue. Back to the ammo again. __________________ ----

August 13, 2016, 12:58 PM	#25
marine6680 Senior Member Join Date: July 24, 2012 Location: Parker, CO Posts: 4,594	Sometimes an AR can be a little tight at first. With a new BCG this may be the case. If after 100rds, it does not clear up and run smoother, double check for binding and other issues like headspace, as it may be on the tight side.