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One reason they chrome plate the chamber and bore, is polymer coated steel cases and of course copper washed steel cased bullets, of the older variety.
If your chamber is not chromed, try cleaning it and the locking lus and recesses, and maybe the gas tube.
May not solve the problem but give it a try.
Another one as others mentioned with many different magazines is quality and specs.
Recoil spring and buffer may help but hammer, maybe not. Your problem is chambering not weak firing pin strike. I definately would not turn down the firing pin, If I understand what you did. As to firing pin weight, not a problem, but titanium pins are available and spring kits to keep firing pin from setting off a too sensitive primer.
I have no idea of specs of old Soviet block steel cased ammo, but you are having, though less, some problems with brass cased ammo. Might get go and no go gauges and loaded round gauge and check that out.
Other than that smoothness of engagement of bolt and locking recesses, or crud.
 

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Discussion Starter · #22 ·
If brass is doing it as well than here is something else wrong. Again , what gas length and weight buffer are you running. As for the rifle failing, what exactly is it doing , failure to feed, failure to eject, failure to fire?
I do not know what gas length. As I said I bought the upper used at a gun show.
I do not know the weight of the buffer. It came from a kit to build s 5.56 lower.
It feeds fine, it ejects fine, if I push the forward assist forward it shoots more times than not.
 

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Discussion Starter · #23 ·
One reason they chrome plate the chamber and bore, is polymer coated steel cases and of course copper washed steel cased bullets, of the older variety.
If your chamber is not chromed, try cleaning it and the locking lus and recesses, and maybe the gas tube.
May not solve the problem but give it a try.
Another one as others mentioned with many different magazines is quality and specs.
Recoil spring and buffer may help but hammer, maybe not. Your problem is chambering not weak firing pin strike. I definately would not turn down the firing pin, If I understand what you did. As to firing pin weight, not a problem, but titanium pins are available and spring kits to keep firing pin from setting off a too sensitive primer.
I have no idea of specs of old Soviet block steel cased ammo, but you are having, though less, some problems with brass cased ammo. Might get go and no go gauges and loaded round gauge and check that out.
Other than that smoothness of engagement of bolt and locking recesses, or crud.
I have done a thorough cleaning and it shoots good until about 10 rounds.
I only took 2/1000th off the firing pin stop.
The have ordered a new enhanced firing pin and the wife says it has arrived.
I'm away at work and won't be home for awhile yet. When I get home I will install the new firing pin, hopefully that will eliminate one part of this perplexing problem.
 

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I do not know what gas length. As I said I bought the upper used at a gun show.
I do not know the weight of the buffer. It came from a kit to build s 5.56 lower.
It feeds fine, it ejects fine, if I push the forward assist forward it shoots more times than not.

Carbine is 7", mid length is 9", and rifle is 12". Just eyeball it with a ruler or measuring tape . For the buffer use a scale and check for the following Buffer Weights
Carbine Buffer (Avg 3.0 oz)
Heavy (H) Buffer (Avg 3.8 oz)
H2 Buffer (Avg 4.7 oz)
H3 Buffer (Avg 5.6 oz)
Rifle Buffer (Avg 5.0 oz)
Believe it or not this might not be the exact issue but I could overall improve the dependability and reduce wear and tare on your rifle. I see a lot of people not understanding the need to adjust buffer wight based on configuration of the upper.
 

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Have you checked the function of the ejector? Making sure it moves freely with just the intended spring resistance.

Just thinking the ejector may not be compressing completely sometimes, then a tap of the FA lets it go into battery.

Can't hurt to remove the ejector, clean, inspect, etc.

Good luck, chasing Gremlins on these things can be frustrating.


Sent from a phone I can use to do my taxes, but can't make a damn call.
 

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Discussion Starter · #26 ·
Carbine is 7", mid length is 9", and rifle is 12". Just eyeball it with a ruler or measuring tape . For the buffer use a scale and check for the following Buffer Weights
Carbine Buffer (Avg 3.0 oz)
Heavy (H) Buffer (Avg 3.8 oz)
H2 Buffer (Avg 4.7 oz)
H3 Buffer (Avg 5.6 oz)
Rifle Buffer (Avg 5.0 oz)
Believe it or not this might not be the exact issue but I could overall improve the dependability and reduce wear and tare on your rifle. I see a lot of people not understanding the need to adjust buffer wight based on configuration of the upper.
Based on this what weight buffer should I use?
 

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Discussion Starter · #27 ·
Have you checked the function of the ejector? Making sure it moves freely with just the intended spring resistance.

Just thinking the ejector may not be compressing completely sometimes, then a tap of the FA lets it go into battery.

Can't hurt to remove the ejector, clean, inspect, etc.

Good luck, chasing Gremlins on these things can be frustrating.


Sent from a phone I can use to do my taxes, but can't make a damn call.
I will remove the ejector and give it a good cleaning.
The has been frustrating to say the least!
 

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Based on this what weight buffer should I use?

Assuming you have a carbine gas system on a 16" barrel a 3.6 oz (H) buffer would be ideal. If it is a mid length gas system on a 16" barrel, a 3oz buffer would be ideal. But being that it's 7.62x39 with a little more gas pressure, maybe need to go one heavier on both lengths. When you shoot, watch where your shells are ejecting. That will give you an idea if the system is balanced right. Slope Font Parallel Magenta Circle
 

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There are 3 parts in the 7.62 x 39 AR that aren't compatible with the 5.56: the barrel, the bolt, and the magazine. I would start with those before troubleshooting anything else. I suspect you might have a Frankenguns upper, and if that's the case, you might have a time finding your fault.
 

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There are 3 parts in the 7.62 x 39 AR that aren't compatible with the 5.56: the barrel, the bolt, and the magazine. I would start with those before troubleshooting anything else. I suspect you might have a Frankenguns upper, and if that's the case, you might have a time finding your fault.

That's what I originally said. But he bought the upper used at a gun show. Makes you wonder why somebody would sell it in the first place? A lot of people struggle to make a 7.62x39 work right. Maybe it didn't work for the last guy either. This is a finicky caliber for an AR. I got mine dialed in and running perfect. I personally would tear it down and inspect the barrel extension, and see how the bolt is locking into the chamber. Possibly getting the chamber polished. I also think the bolt might be the problem. This bolt from SOTA Arms has been good to me .

https://www.sotaarms.com/component/...120511234447120528200444120528222545?Itemid=0
 

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That's what I originally said. But he bought the upper used at a gun show. Makes you wonder why somebody would sell it in the first place? A lot of people struggle to make a 7.62x39 work right. Maybe it didn't work for the last guy either. This is a finicky caliber for an AR. I got mine dialed in and running perfect. I personally would tear it down and inspect the barrel extension, and see how the bolt is locking into the chamber. Possibly getting the chamber polished. I also think the bolt might be the problem. This bolt from SOTA Arms has been good to me .

https://www.sotaarms.com/component/...120511234447120528200444120528222545?Itemid=0
I've used SOTA barrels on builds and I only have good things to say about them. Great barrels at a great price. I've also used Doublestar parts before, and sometimes they have a breaking in period. I wouldn't personally have bought a complete upper from a gun show dealer unless he represented a easy to get to business. Getting back to the OP, I would check the bolt first, then look at the barrel. I would also look at getting a different magazine. That would be the cheapest part to replace. If he can remove the barrel, maybe there is something wrong with the receiver itself being out of spec, not likely, but possible.
 

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Discussion Starter · #32 ·
First, I want to thank everyone that has commented on this. I should have said right off the bat that I have only owned the AR platform for a short period of time now and am learning as I grow with these rifles (I have a Omni Maxx 5.56 as well).
I have not done a complete upper build yet so, I'm still learning in that aspect.

I have decided to start from the back and work my way forward. I have ordered a David Tubb flat buffer tube spring and a Spikes Tactical TS-T2 buffer to be installed when I return home in about a week. Hopefully this will take some of the problem out of the equation.

I plan on doing a thorough cleaning once again during the new spring and buffer install.
 

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One thing that was not talked about is the Bolt Carrier. The .762 will need a full mass bolt carrier, like what is used on the full auto .556. A low mass bolt carrier will not have enough forward energy to strip the .762 round out of the mag and then lock into the barrel correctly. This sounds like what you are experiencing. With both steel and brass giving you trouble (the steel will be worse because they produce more friction or drag than brass does).
If you are having to use the forward assist then your weapon is not locking in full.
After you install the new spring and buffer you still have trouble, take a look at the bolt carrier, the lugs on the bolt and the barrel lugs. Any small burr will cause problems.
In any case using the forward assist is not something you should be doing all the time. This is an indication that your weapon needs a "Qualified" gun smith to check it out.
 

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Discussion Starter · #34 ·
Update-

I installed the new spring and buffer. It now shoots the brass cased ammunition flawlessly. I'm still experiencing a few FTF's with the steel cased ammo.
I have exhausted my limited knowledge on this platform. It is now slated to go to the "gun doctor".

Thanks to all that tried to help.
 

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Discussion Starter · #35 ·
First let me say this is going to be painful to tell this-

When I first bought the upper it ran flawlessly...for awhile. Then things started to progressively get worse. It wouldn’t feed correctly, eject, fire, ect. It would strike the primers but not fire. I bought stiffer hammer springs, enhanced firing pins, flat buffer springs, a heavier buffer. Hell I even bought an enhanced BCG, NOTHING made this rifle shoot properly. I even took it to a gunsmith and he fixed the headspace problem but the rifle still would not run a full mag without some kind of problem. So I thought maybe it was the magazines so I took some concrete nippers and smoothed the ribs down inside the mags thinking that the bullets were hanging ever so slightly on them. I dremeled the front of the mags down in front of the followers thinking the case neck might be catching there and slowing the feeding action down. Nope, didn’t help. I got disgusted and put the thing in the safe and walked away from it bound and determined to get rid of it.

So, I was in that safe getting a 5.56 out and there it was...I thought about it and from the last round of major disappointment with it, I said to myself why not take the gas system off and clean it? So I did. During the last step of putting the BCG back in I reached over to grab it and picked it up by the gas key...IT WAS LOOSE!!!!! I thought you have got to be kidding me! This can’t be it! After all the **** I have been through with this gun! Hell the bolts were even staked!

Now comes the painful part. That was the problem all along. I tightened the heck out of the bolts put the gun back together. Loaded a mag with steel cased ammo and shot it slowly. Not one hiccup! Loaded another mag and did a mag dump. Not one hiccup! I’m relieved but a little pissed at myself at the same time.

In my own defense all I can say is that my lack of knowledge of the AR platform was the biggest factor for all of this. Some of you might be asking yourselves “why would he post this on a public forum about his ineptitude“? All I can say to that is- if I can help one person from going through what I went through then it is worth it.
 

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Glad you got it figured out Artie.
I have a Palmetto AR ( takes AK mags) and 2 Mini-30's.
I've been testing lots of different brands of steel case ammo, and one thing I can tell you:
There are lots of decent steel case loads out there, but Tula/Wolf aren't one of them.
99% of the forum posts I see where a guy is complaining about accuracy, ignition, chambering or dirty A%# steel case ammo, he mentions he is using Tula ( or Wolf).
Do your self a favor and try some Red Army Standard Boat tail, or Silver or Golden Bear.
Cleaner, more accurate, around 150-200 fps. faster, and zero ignition problems out of AR's or Mini's in x39.
 

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First let me say this is going to be painful to tell this-

When I first bought the upper it ran flawlessly...for awhile. Then things started to progressively get worse. It wouldn’t feed correctly, eject, fire, ect. It would strike the primers but not fire. I bought stiffer hammer springs, enhanced firing pins, flat buffer springs, a heavier buffer. Hell I even bought an enhanced BCG, NOTHING made this rifle shoot properly. I even took it to a gunsmith and he fixed the headspace problem but the rifle still would not run a full mag without some kind of problem. So I thought maybe it was the magazines so I took some concrete nippers and smoothed the ribs down inside the mags thinking that the bullets were hanging ever so slightly on them. I dremeled the front of the mags down in front of the followers thinking the case neck might be catching there and slowing the feeding action down. Nope, didn’t help. I got disgusted and put the thing in the safe and walked away from it bound and determined to get rid of it.

So, I was in that safe getting a 5.56 out and there it was...I thought about it and from the last round of major disappointment with it, I said to myself why not take the gas system off and clean it? So I did. During the last step of putting the BCG back in I reached over to grab it and picked it up by the gas key...IT WAS LOOSE!!!!! I thought you have got to be kidding me! This can’t be it! After all the **** I have been through with this gun! Hell the bolts were even staked!

Now comes the painful part. That was the problem all along. I tightened the heck out of the bolts put the gun back together. Loaded a mag with steel cased ammo and shot it slowly. Not one hiccup! Loaded another mag and did a mag dump. Not one hiccup! I’m relieved but a little pissed at myself at the same time.

In my own defense all I can say is that my lack of knowledge of the AR platform was the biggest factor for all of this. Some of you might be asking yourselves “why would he post this on a public forum about his ineptitude“? All I can say to that is- if I can help one person from going through what I went through then it is worth it.
I've ran into that problem when troubleshooting a customer's AR. I replaced both the key and the screws, torqued them to spec, then staked the screws. That is the only way to correct the problem.
 
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I have same setup, 7.62 on a Ar-15 lower, and it will not load next round, standard carbine length buffer spring, and buffer (3oz) Tulammo steel cases 122g, AR stoner 10 round mag, I could use some guidance??! Brand new build
Thanks anyone👍
 
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