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Old 11-14-2016, 09:08 AM   #1
Rob Ski
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Default IMPORTANT UPDATE about Zastava NPAP 5k rounds rifle

IMPORTANT UPDATE about Zastava NPAP 5k rounds rifle: guys, one of the members spotted small cracks developing on the back of the receiver of NPAP rifle in our last Zastava video.
I have checked pictures from early runs and those cracks weren't there (included is picture from 1st video, after 1k rounds).
Now, after 5k rounds, you can see 2 cracks around cover button hole (see bottom picture).
Thanks for bringing this to my attention.

Ps. i know that there is a thread going on zastava video, but i think that this update deserves separate discussion.

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Old 11-14-2016, 09:17 AM   #2
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Well I remember Battlefield Las Vegas saying the npaps never held up. I forgot which part they said usually would give.
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Old 11-14-2016, 09:25 AM   #3
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Location is everything.

The cracks in the indicated spots are not surprising, as they have spawned in a weak area ( and there's no way around the "weak area" due to the chosen design )

If the recoil spring locking mechanism weren't there, I highly doubt there'd be any cracking.


( this is why it's suggested that folks weld up their Klinton holes after converting a Saiga )
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Old 11-14-2016, 09:32 AM   #4
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Quote:
Originally Posted by Tankboy View Post
Well I remember Battlefield Las Vegas saying the npaps never held up. I forgot which part they said usually would give.
If my memory serves me correctly, it was because of cracks in the receivers just like this. Although I don't know if it was at the rear trunnion area or not.

Found this after a quick search. Ron from Battlefield Vegas said this:
"– Stamped receivers split at the angle of the upper rail and the side wall. N-PAP’s have literally cracked in half perpendicular to the length of the rifle. The receivers cracked just posterior of the front trunion (between center bushing and the trunion)."

Got that quote from the following link.
http://www.thefirearmblog.com/blog/2...t-breaks-down/

For what it's worth Ron also added this...."– Every single stamped receiver has suffered from a cracked trunion. This includes Saiga, Arsenal (Bulgarian), Norinco (Chinese), Arsenal (Russian stamped), WASR, Hungarian, Polish (vintage kits), Yugo (vintage and PAP-series) and new Polish (from Royal Tiger imports)."
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Old 11-14-2016, 09:37 AM   #5
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Not surprised.

Technically I WAS surprised it made it to 5,000
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Old 11-14-2016, 09:38 AM   #6
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Battlefield vegas mentioned they had to replace stocks on the very first day of use...so they go ahead and replace them as soon as they arrive...
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Old 11-14-2016, 09:39 AM   #7
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I saw that crack. So that means I was right?
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Old 11-14-2016, 09:40 AM   #8
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The cracks on BLV were vertical just behind the front trunnion

http://www.ar15.com/forums/t_4_64/15...1_.html&page=2

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Old 11-14-2016, 09:47 AM   #9
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Quote:
Originally Posted by nalioth View Post
Location is everything.

The cracks in the indicated spots are not surprising, as they have spawned in a weak area ( and there's no way around the "weak area" due to the chosen design )

If the recoil spring locking mechanism weren't there, I highly doubt there'd be any cracking.


( this is why it's suggested that folks weld up their Klinton holes after converting a Saiga )
Good to know. Thanks
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Old 11-14-2016, 09:55 AM   #10
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Shiite
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Old 11-14-2016, 09:57 AM   #11
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Originally Posted by Sn1p3r_1 View Post
I saw that crack. So that means I was right?
Well obviously.
On the same token, do you still think that our videos are "entertainment only"?
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Old 11-14-2016, 09:57 AM   #12
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Originally Posted by sp1in3 View Post
Battlefield vegas mentioned they had to replace stocks on the very first day of use...so they go ahead and replace them as soon as they arrive...
that's on the new wasrs they get

the armorer mispoke in the video and said yugos

BLV hasn't had any yugos since original batch that went to shit
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Old 11-14-2016, 10:02 AM   #13
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Quote:
Originally Posted by Rob Ski View Post
Well obviously.
On the same token, do you still think that our videos are "entertainment only"?
Good question.
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Old 11-14-2016, 10:34 AM   #14
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I will NEVER buy an NPAP. Too many quality offerings out there including new U.S. made PSA and DDI AK's. 5,000 rounds ain't nothing for this to happen.
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Old 11-14-2016, 11:07 AM   #15
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Quote:
Originally Posted by Rob Ski View Post
Well obviously.
On the same token, do you still think that our videos are "entertainment only"?
They are entertaining and informative on what a rifle can do on more than range trips but the tests are not always the same. I understand it's hard to do the control.

You keep doing what you are doing. Lots of guys here like what you do.
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Old 11-14-2016, 11:15 AM   #16
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Mentioned this in the other thread, will mention it here since it now has it's own dedicated thread.

The FTF were likely caused by a weak recoil spring. Weak recoil spring = rear trunion getting beat to shit. Which is likely why the top cover retainer became loose and fell out.
Not putting it back in left an un-supported hole right next to another hole leading to the crack.

No idea if it would have eventually happened anyway. But, it sure was accelerated by the above two things.

Last edited by moshaholic2; 11-14-2016 at 09:13 PM.
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Old 11-14-2016, 11:22 AM   #17
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Damn. That's some crazy shit. "You can't make this kind of shit up." I now will buy the N PAP's suck.
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Old 11-14-2016, 11:22 AM   #18
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Quote:
Originally Posted by Martensite View Post
I will NEVER buy an NPAP. Too many quality offerings out there including new U.S. made PSA and DDI AK's. 5,000 rounds ain't nothing for this to happen.

I'd be curious to know if just removing/not using the lock mechanism would reduce the damage in the area...



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Old 11-14-2016, 11:28 AM   #19
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Cut it up and hardness test it!
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Old 11-14-2016, 11:34 AM   #20
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Quote:
Originally Posted by Sabre5G View Post
Damn. That's some crazy shit. "You can't make this kind of shit up." I now will buy the N PAP's suck.
Any AK with a similar setup would likely have cracked around the same time frame.

The area where the cracks are are weakened by the two holes ( recoil spring lock & rivet ) in close proximity to the end of the plate.

Quote:
Originally Posted by NorincoKid View Post
I'd be curious to know if just removing/not using the lock mechanism would reduce the damage in the area...
For anyone who has the most basic knowledge of material strengths, stressors, etc, the answer is "yes, it would likely not have cracked at 5K without the recoil spring lock shaft"
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Old 11-14-2016, 11:59 AM   #21
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I can understand those holes being a high stress area prone to cracks like shown, but I also wonder if using the rifle while the holes are empty(spring loaded retaining pin removed like done here) sped up the appearance of those stress cracks. This is pure conjecture here but if that space had been spanned properly with that pin maybe this wouldn't have happened. Also, the reduction in rear trunion rivets on the newer models can't be helpful to the situation either.

Seems to me the structural integrity of the receiver would be compromised in this area of the NPAP more so than with the Saiga conversion holes because of proximity to the heavy BCG reciprocating mass during live fire on the NPAP.
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Old 11-14-2016, 12:05 PM   #22
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Has anyone seen a Saiga crack around the sporter fcg holes? Not saying it isn't possible, but I've never heard of that happening to anyone.
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Old 11-14-2016, 12:06 PM   #23
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Quote:
Originally Posted by GGGultimateAK View Post
I can understand those holes being a high stress area prone to cracks like shown, but I also wonder if using the rifle while the holes are empty(spring loaded retaining pin removed like done here) sped up the appearance of those stress cracks. This is pure conjecture here but if that space had been spanned properly with that pin maybe this wouldn't have happened. Also, the reduction in rear trunion rivets on the newer models can't be helpful to the situation either.

Seems to me the structural integrity of the receiver would be compromised in this area of the NPAP more so than with the Saiga conversion holes because of proximity to the heavy BCG reciprocating mass during live fire on the NPAP.
For the holes to not have been stressed, the innards would have to've been tight enough not to be functional, so "yep, cracks away!"


As I mentioned earlier, with this design choice, stress cracks are gonna show up early ( compared to standard AKM receivers )
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Old 11-14-2016, 12:07 PM   #24
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It's almost fascinating on how they came up with this design to reinforce the top cover from having to withstand a grenade lobbing and all......and as it turns out it's the opposite, a weaker spot in the entire receiver. If anything, it'll do the opposite, it will fall apart after only a few grenades (not that NPAP was actually made to lob grenades).

As pointed out, the material between rivet and dust cover pin is very marginal and it's a weak link for sure.

Never liked Yugos, never bought any and imo they never fit in to a true AK, starting with non chrome line barrel.
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Old 11-14-2016, 12:12 PM   #25
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Cut it up and hardness test it!
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Old 11-14-2016, 12:31 PM   #26
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Quote:
Originally Posted by Bacon&AlcoholDistributor View Post
It's almost fascinating on how they came up with this design to reinforce the top cover from having to withstand a grenade lobbing and all.
It's actually designed to keep the bolt carrier group from rearranging your body parts when a grenade is launched.

Also keep in mind that the military can afford to replace Ivan the grenadier's AK when it breaks, and wear is expected.
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Old 11-14-2016, 12:35 PM   #27
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Welcome!

To total drama island!
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Old 11-14-2016, 12:40 PM   #28
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This thread will go on for pages.
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AK barrels hardness testing results.
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Old 11-14-2016, 12:43 PM   #29
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This thread will go on for pages.
Ages. Not pages.
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Old 11-14-2016, 12:46 PM   #30
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I recently bought a N-Pap DF and I have been watching this thread with great interest. I am not new to AK-s having bought my first in the 1980's.

My N-Pap has approx. 300 rounds through it and has been a pita. I have replaced the weak recoil spring, had to loctite the front sight pins to keep them from walking out, and I am in the process of replacing the Mickey-mouse cleaning rod with a surplus Polish, as the Yugo one walks out. That said, my N-Pap has performed very well as far as no firing malfunctions, and very accurate. I am generally happy with mine, until I read about the cracking.

I chose an N-Pap to purchase as they have been on the market for many years, and while reviews were mixed, most were positive.

A few questions: should be lots of N-Paps out there with more than 5,000 rounds through them. Any other reports of receiver cracks?

Could the crack have been caused or started by the torture test Rob uses?

I have no opinion on these questions, just seeking opinions from the many knowledgeable folks here.
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Old 11-14-2016, 12:48 PM   #31
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Quote:
Originally Posted by Bacon&AlcoholDistributor View Post
It's almost fascinating on how they came up with this design to reinforce the top cover from having to withstand a grenade lobbing and all......and as it turns out it's the opposite, a weaker spot in the entire receiver. If anything, it'll do the opposite, it will fall apart after only a few grenades (not that NPAP was actually made to lob grenades).

As pointed out, the material between rivet and dust cover pin is very marginal and it's a weak link for sure.

Never liked Yugos, never bought any and imo they never fit in to a true AK, starting with non chrome line barrel.
Don't make too broad a generalization over one rifle and one instance.
Of course the 1.5mm receivers would be more durable.
I have de-milled a pretty large number of Zastava rear blocks., admittedly mostly 1.5mm and never saw a cracked area at the receiver cover locking area. Dunno.
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Old 11-14-2016, 12:59 PM   #32
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Quote:
Originally Posted by GGGultimateAK View Post
Also, the reduction in rear trunion rivets on the newer models can't be helpful to the situation either.
Were there any issues/reports of cracking at that point on the older versions with 3 rear rivets?
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Old 11-14-2016, 01:00 PM   #33
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MIGHTY WASR > NPAP

The Mighty WASR wins again.
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Old 11-14-2016, 01:15 PM   #34
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It is a very very small crack and so far has not interrupted function.
If anything you could spot weld it up for reinforcement.
No need to start panicking.
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Old 11-14-2016, 01:27 PM   #35
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Quote:
Originally Posted by ninjamateo View Post
It is a very very small crack and so far has not interrupted function.
If anything you could spot weld it up for reinforcement.
No need to start panicking.


Exactly.
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