Author Topic: Popped Primer Problem (update 6-28-13 Found a CURE)  (Read 67577 times)

0 Members and 1 Guest are viewing this topic.

FJRrider

  • SKS Marksman
  • ***
  • Posts: 103
Re: Popped Primer Problem
« Reply #15 on: March 17, 2013, 05:28:37 PM »
Update time! (With pictures)

After my previous posts about the popped primers I was contacted by the nice folks at Murray's who said they have a solution beyond just smoothing out bolt face. Since I'm all about trying new things and was offered a good deal on having them do the work (both their new idea and the bolt face modification), I shipped off my barreled receiver and bolt/carrier/firing pin to them.

I'm not an expert on what they did but in a nutshell it goes a little something like this:

Mr. Murray had done some research on certain .223 guns having issues with handling the hotter 5.56 rounds. Apparently the answer was to "open" the "throat" or "leade" of the barrel (the part in front of the chambered cartridge where the bullet itself rests) which then allowed more room for the gases to escape. (I apologize if I'm butchering the explanation as I only have a rudimentary knowledge of any of this).

Mr. Murray, Ben to his friends and customers, thought "if it works for .223/5.56 then it should also work for 7.62 in an SKS". Would opening up the throat a bit lead to a loss of accuracy? Maybe, but since the SKS isn't a tack-driver anyway it probably wouldn't be noticeable to any mere mortal.

This "throat mod" is the new, ultra-secret modification that Ben references in the post directly above this one. He'd only done a couple so I was part of the guinea pig group.

I can't show any pictures of the "throat mod" (was going to call it a "throat job" but didn't for obvious reasons) because I don't have a bore scope but I will show pics of the bolt face mod.

Before


After


So did it work?

Since we didn't do this test scientifically (we changed two things at the same time instead of one and test then the other and test) I can't tell you what made the biggest difference - the throat mod or the bolt face mod. What I can tell you is this - the first time I shot the gun I got through 5 rounds of Wolf Polyformance FMJ before the first failure to fire (light primer strikes) due to pieces of primer wedging into the firing pin channel (figured that part out later). In total I had about a 20% non-fire rate out of 50 rounds cycled.

After the mods I went out and shot 20 rounds: 10 rounds of Wolf Polyformance FMJ (on left) and 10 rounds of this cheap, corrosive ammo I picked up (on right):


Fired slow, fired fast and not one popped primer or light primer strike at all. The SKS shot through all 20 rounds like a champ and at 25 yards with the stock sights in a poorly lit range shooting at a small target all 20 rounds found their mark.

I'll let Ben explain the details better but it would seem that he's on to something with both the bolt face mod and the throat mod.

Rocketvapor

  • Board Supporter
  • SKS Guru
  • *****
  • Posts: 15076
  • awarded title of SIR ARSE
Re: Popped Primer Problem
« Reply #16 on: March 21, 2013, 04:18:19 AM »
Does anyone think that the deep set primers on certain brands of ammo is a likely cause of the problems here?
When you look at cratering of primers, popped primers, volcano-ing of the bolt face, it seems the large unsupported area of the primer itself is a potential cause. 
Murray's positive stop firing pin can't volcano a bolt face from dry firing. Just can't.  Does it still happen?
Do primers still crater (significantly)? Why? Champhering the bolt face delays the volcano but primers still crater.  You can't reduce the pin strike depth much with these deep set primers, or you lose reliable firing. 

The PSI applied by a firing pin strike is quite high.  Radially out from the pin strike is the cup section of the primer.  Further out from there is the flange of the cup, and further still the base of the case.  A deep set primer has lots of unsupported area and we know what happens when a case isn't properly supported.  Is the volcano formed when the unsupported primer area strikes back at the bolt?

Do boxer primed cases have the same problems? Or, are we just afraid to use them with an inertial pin bolt? 

Nothing but questions, I know.


 
Well I guess my new **** stirrin paddle don't work . I got a like . WTF 😈

Flo just received her EXPERT Mid range card from the NRA.

https://www.yahoo.com/news/famed-ex-uss-john-f-003916449.html

murray

  • Life Member
  • SKS Gunsmith
  • *****
  • Posts: 2052
    • https://murraysguns.com
Re: Popped Primer Problem
« Reply #17 on: March 21, 2013, 05:19:01 PM »
Thanks for the update FJRrider! Excellent write up. And we intend to call this not really so ultra-secret service a "Neck & Throat" mod. The "Neck" of the chamber, where the bullet is seated in the case, is opened just a thousandth or two in diameter, and the Throat, or "leade" where the bullet sits when a cartridge is loaded in the chamber, just in front of the forward end of the case, has the angle reduced and lengthened.

We're still testing, and receiving reports from our guinea pigs. ("Testers" sounds much better)  And it does look promising so far. The shoulder that headspace is measured from is Not cut at all so this has absolutely No effect on the headspace.

Rocketvapor, the deep set primers don't help any, but I don't think that is a major contributing factor. But the "unsupported" area of the primer is problematic. AKs have an approximate .080 diameter FP hole, and SKSs have .090 to .095. We feel this may be part of the reason SKSs have the problem much more than AKs. But addressing the spikes in the peak chamber pressure does seem to have a more positive effect than just addressing the FP hole size/unsupported area of the primer.

We have only heard of one case of popped primers with Boxer primed ammo. And that case is suspicious as we never saw the empty case in question. So for the most part, yes, this is a problem involving the Russian imported Berdan primed ammo only, and you'll not experience the problem with Boxer primed ammo. Most people use the Berdan primed stuff simply because it is cheap, compared to Boxer primed.

https://murraysguns.com/shop/

If you feed it junk ammo, why should you expect filet mignon results? Well now you can, with our new "Neck & Throat" chamber reaming service!

rj308

  • SKS Newbie
  • Posts: 26
Re: Popped Primer Problem
« Reply #18 on: April 08, 2013, 11:18:22 PM »
As I posted in the Yugo forum, I installed a "finger pressure" FP retaining pin in  my Yugo's bolt. It is kept from backing out and rotating by a small glob of high strength epoxy on the retaining pin tab. The glob of epoxy takes up the clearance between the bolt and bolt carrier so the pin does not back out laterally. This is so I can clean the firing pin and its channel in the bolt after a shooting session without having to pound out the retaining pin, and risking damage to it or the bolt. As I have found out for myself lately, SKS parts are no longer plentiful or cheap.

bruss01

  • SKS Marksman
  • ***
  • Posts: 116
Re: Popped Primer Problem
« Reply #19 on: May 25, 2013, 12:25:19 PM »

I had this same issue with an x39 AR-15, using MGI's Reliability Bolt.  Once the FP hole edge was relieved a bit, no more cookie-cutter brass disks in my firing pin channel.


murray

  • Life Member
  • SKS Gunsmith
  • *****
  • Posts: 2052
    • https://murraysguns.com
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #20 on: June 28, 2013, 03:30:06 PM »
That's right, we edited the title of this thread and will soon make an announcement of offering this service to everyone, but for now, we're offering  the first 6 people that would like the service for free, and report here as Beta testers of sorts, a new "Neck & Throat" reaming procedure to the chamber portion of the barrel. This does not change the headspace AT ALL, but so far has proved Very successful at eliminating the pesky popped primers when shooting Berdan primed ammo.

The first 6 to send a PM or email saying "I want the free N&T job" will be supplied a copy of our FFL so the barreled receiver can be shipped to us legally, and you will only be asked to pay $20.00 for return shipping, and report to us or here at the Boards about your subsequent range trips and whether or not you experienced any more popped primers. (time stamps apply)

Later on, we expect the service to have a nominal $30.00 to $35.00 charge. (+ return shipping)

Here's a chance at being able to shoot any and all ammo available with much more confidence, so you better jump on it quick.

« Last Edit: September 27, 2013, 10:42:04 AM by murray »
https://murraysguns.com/shop/

If you feed it junk ammo, why should you expect filet mignon results? Well now you can, with our new "Neck & Throat" chamber reaming service!

dgag

  • SKS Newbie
  • Posts: 4
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #21 on: July 22, 2013, 03:39:15 PM »
Hey Ben,
I talked to you earlier today over the phone.  I field stripped my SKS and am sending my barreled receiver to you for the N&T reaming in the AM.

A little history...I had sent my SKS bolt and firing pin to Murray's Gunsmithing to receive Ben's 2013 modifications.  A New spring loaded firing pin and machined bolt.  I put it back in my SKS awhile ago and last week found time to take it to the range.

I put 120 rnds through it and noticed that the firing pin was slightly sticking out of the bolt face and had the tip wrapped in primer brass.  Yes these rnds had berdan primers.  I field stripped the bolt and indeed found primer brass as well as a mangled spring!!!

Simply stated There is still a problem and potential for a slam fire if you shoot berdan primed ammo. Hopefully the N&T reaming will do the trick.  I am going to serve as a Beta tester once I get my barreled receiver back.  I'll keep everyone up dated.
Thanks,
Dgag

dgag

  • SKS Newbie
  • Posts: 4
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #22 on: July 22, 2013, 04:09:46 PM »
Hi guys,
I can already hear the question!!!!  If this problem only occurs with berdan primers why shoot this ammo?  Well the answer is simple.  If you have several thousand rnds of this ammo....what are you going to do?

I certainly will not sell it to some unsuspecting person.  Nor will I ever buy any more.  My SKS on an intrafuse Bayonet stock was zeroed at 100 yds but still exhibited occasional flyers.  Don't know if the ream job will affect accuracy or not.  This will also be reported on when I get the barreled receiver back.  Thanks
dgag

murray

  • Life Member
  • SKS Gunsmith
  • *****
  • Posts: 2052
    • https://murraysguns.com
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #23 on: July 22, 2013, 04:19:55 PM »
None of our testing has shown any change in accuracy. And we didn't decide to even try this until we saw the following Weatherby chart. (guns that are known to easily shoot 1" @ 100 yds)

Cartridge                 Throat length (free bore)
.224 Weatherby Magnum      .162
.240 Weatherby Magnum      .169
.257 Weatherby Magnum      .378
.270 Weatherby Magnum      .378
7MM Weatherby Magnum      .378
.300 Weatherby Magnum      .361
.340 Weatherby Magnum      .373
.375 Weatherby Magnum      .373
.378 Weatherby Magnum      .756
.416 Weatherby Magnum      .239
.460 Weatherby Magnum      .756
.30-378 Weatherby Magnum .361
.338-378 Weatherby Magnum .361

Hard to believe that a chamber with 3/4" of freebore could achieve that sort of accuracy, but there it is. We only extend the leade in the SKS chamber about .250.



https://murraysguns.com/shop/

If you feed it junk ammo, why should you expect filet mignon results? Well now you can, with our new "Neck & Throat" chamber reaming service!

pinhead1979

  • SKS Expert
  • ****
  • Posts: 269
  • Defiler Of C&R Rifles
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #24 on: July 23, 2013, 10:06:58 AM »
I can already hear the question!!!!  If this problem only occurs with berdan primers why shoot this ammo? 

Same reason most people shoot it... 5 bucks for 20 is a hell of a lot easier on the wallet than 30 bucks for 40. Po' folks wanna shoot too!  :)

Just got mine back from Ben as well. Range report within the week.

Rocketvapor

  • Board Supporter
  • SKS Guru
  • *****
  • Posts: 15076
  • awarded title of SIR ARSE
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #25 on: July 23, 2013, 02:23:41 PM »
I can already hear the question!!!!  If this problem only occurs with berdan primers why shoot this ammo? 

Same reason most people shoot it... 5 bucks for 20 is a hell of a lot easier on the wallet than 30 bucks for 40. Po' folks wanna shoot too!  :)

I guess run away boxer primed ammo would be better?
If there's something wrong with your SKS, which problem would you rather have?
Well I guess my new **** stirrin paddle don't work . I got a like . WTF 😈

Flo just received her EXPERT Mid range card from the NRA.

https://www.yahoo.com/news/famed-ex-uss-john-f-003916449.html

murray

  • Life Member
  • SKS Gunsmith
  • *****
  • Posts: 2052
    • https://murraysguns.com
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #26 on: July 23, 2013, 06:26:41 PM »
Quote
which problem would you rather have?

Actually RV, we would prefer "Neither!"

First, we don't believe that "inertial power" of a free floating FP has ever been proved to be the cause of slam fires or unintentional full auto. (even with Boxer primed ammo) The FP needs to stick hard in a forward position for there to be any chance of this happening. But that often happens to free-floating FPs when using the Berdan primed ammo, and popped primer pieces get in the way. So we recommend installing our FP which actually addresses both issues, and no one has ever experienced slam fire or unintentional full auto with our FP. Even when popped primers occur with our FP. It may ruin the spring, and the pieces of primers can cause misfires, but no serious problems have ever occurred.

And the post we made above (6-28) is the news that we have discovered a cure for those pesky popped primers. And the cure simply reduces the spikes in the peak chamber pressure, and stops the primer pieces from being blown into and often through the FP hole.

So we wouldn't say there is something "wrong" with any SKS, except that with the currently imported Russian Berdan primed ammo, more leade, or as described by some, a longer freebore is what it takes to shoot that stuff without worries. (too bad we can't get the same ammo that our enemies use in the sandbox, I've seen it and it's much better quality than the Russian stuff we see here)

And that is what we have always strived for. Fine tuning so you don't have issues while trying to enjoy yourself at the range.

While some may strive for accuracy, everyone wants it to go bang every time they pull the trigger. And this new "Neck & Throat" reaming service, combined with our FP Kit, allows SKS owners to expect just that. If the ammo says 7.62X39 on the cartridge, you should be able to shoot it in any SKS, with no worries about slam-fire, misfire, or popped primers. And we have found absolutely no evidence that the reaming of the neck and throat has any effect on accuracy.


https://murraysguns.com/shop/

If you feed it junk ammo, why should you expect filet mignon results? Well now you can, with our new "Neck & Throat" chamber reaming service!

Glassparman

  • SKS Marksman
  • ***
  • Posts: 130
    • Glasspar Owners Association
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #27 on: August 07, 2013, 04:08:54 PM »
One more reason . . . I picked up a box of 5000 Tulammo Berdan primers to reload all those Yugo brass cases we find laying around the range :)

I'm getting mine done now!

Michael
"There is no greater feel than to be in control of 56 tons of steel and watching that 105mm round go down range and blow something up."

agrace

  • Board Supporter
  • SKS Sniper
  • *****
  • Posts: 549
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #28 on: August 23, 2013, 08:37:47 PM »
Sent mine off to have this done today.. will report back on my range trips after this :)

Thanks Ben, can't wait to try it out when you are all done!

agrace
« Last Edit: August 27, 2013, 03:22:13 PM by agrace »
I love the smell of gunpowder in the morning.

jonnyugo

  • SKS Gunsmith
  • *
  • Posts: 1204
Re: Popped Primer Problem (update 6-28-13 Found a CURE)
« Reply #29 on: August 23, 2013, 11:25:25 PM »
One thing that I believe is a part of the problem on Yugo's is that the OE ammo is lead core because of the non-crome barrel. The yugo surplus is a crimped bullet VS the glued style used on steel core/case ammo. The steel case/core ammo in x39 was designed and intended for chrome lined barrels, the Ruskies figured that out in the early SKS development. I have Yugos that have fired case after case of yugo M57 surplus flawlessly then puke out on a bad case of steel. Shoot the same case of steel in my AK, chrome chi-com, no problem? Pulled down really bad case of prime-poppen steel and found case necks with case lac. and bullet sealent (glue) , some worse then others, but there were some glued so tight that I believe these would pop the primer in any rifle. These are seconds, when problems are found during production like this its sold off for the sport shooting market. The popped primer issue is not a one thing problem but several things possibly coming together. At the end of the day, like it or not, the Yugo was engineered and designed for brass case lead core ammo. When you have problems with the yugo surplus, you really have a problem.
« Last Edit: August 24, 2013, 02:36:50 AM by jonnyugo »
The “final, most essential command” of the ruling totalitarian regime is “to reject the evidence of your eyes and ears.”