Hard primers or bad firing pin/spring?

I must comment that your pictures are superb and the firing pin indentations appear sufficient to launch the bullet.
Complaints to the factory may be difficult to make.

I would think hard primer with a semi weak spring. I had the same problem with Tula/Wolf Military Classic in 7.62X39 in my Mini 30. New factory springs made it shoot reliably again. The same ammo was good to go in any of my SKS's though.

That firing pin strike seems shallow in the unfired round to me.

The answer is probably hard (maybe steel) primers, but you could also have dead primers. Will a round that doesn't fire go off on the second try? Have you tried that ammo in any other rifle, like a bolt action?

"Dimpled" primers can be deceiving; very often the dent is deep enough to fire, but since the primer did not fire, the primer metal did not push back around the firing pin, and there is a "dimple" instead of the neat "crater" we are used to seeing. So it is hard to say whether a misfire is the result of too light a firing pin blow or a dead primer.

Another factor could be failure to completely lock up, so the firing pin is not going forward far/hard enough to fire the primer.

FWIW, the AR-10 has a hammer, so if a spring is too light, it would be the hammer spring, not the "firing pin spring".

Jim

Firing a primer has more to do with speed of impact, then how deep the dent is from a slow heavy hammer fall.

As an example, the striker in a Glock pistol weighs little more then a good healthy bugger.
But it moves super fast.

Another example.
You can smash a primer flat in a vice and it won't go off.
(Lots of force, but no speed of impact.)

It follows that you have introduced an unknown variable with the unit trigger group.
So who knows if you are getting the necessary hammer speed to ignite mil-spec hard & less sensitive Russian primers?

I'd put the original parts back in it and start over from square 1 and that will either prove or disprove defective ammo.

Or a defective unitized aftermarket trigger group with insufficient hammer speed.

rc

If those pictures had not been posted, I would have said the usual - everything that has been mentioned. Those strikes appear to be at full depth. The only way a full depth strike can be made is that the firing pin protrusion is correct AND sufficient energy has been imparted to it. If in fact the strikes are at full depth, then the ammo is bad and should be tossed.

Don't make the mistake of comparing primer strikes from a fired case with primer strikes from a misfire. Fired cases will always show more depth because the primer smacks backwards against the f.p. instantly upon firing.

Perhaps the photos exaggerate the depth of the strikes. The first test is to measure f.p. protrusion, which should be part of any final checkout anyway. Then confirm that the hammer spring has not been lightened up to "produce" a lighter trigger pull. Third, and often ignored, is to check headspace. Yes, you want a safe gun with no blowouts. But in this case you are checking to see if the primer is sitting too far forward in the chamber. With springs out of the gun, the bolt should not close on a no-go gauge. Otherwise some of the firing pin energy is spent moving the round forward into the chamber. In the latter case, it is time for a new barrel. In cases like this, you often find that some ammo fires and some does not. That fact is irrelevant. Let us know what you find.

-WM

The single photo looks like a light FP hit to me. I read that military ammo has harder primers to reduce the possibility of slam firing with rifles that have a free-floating firing pin.

"Firing a primer has more to do with speed of impact, than how deep the dent is..." Partially true. The firing pin has to impart sufficient energy to the primer within a defined time period. So, there is the dv/dt part, but also a mass component. For example, a titanium firing pin can be moving a lot faster than a steel firing pin and still not set off a primer. Depends upon the design. I've always been interested to see some graphs depicting variable hammer mass, variable hammer spring weight, f.p. velocity and energy transfer to the primer.

But, the good news is that the method of troubleshooting the problem remains the same.

WM

That would be the first thing you should do!!!

Any time you have a gun or ammo problem??

The very first thing to do is try different ammo.

rc

I would try the rifle with whatever you used when you ran a thousand rounds through it. If it works, stick with that or put the original parts back in and try it again with the Russian ammo. OR, make someone a deal on the Russian and stick with American ammo, or load your own...

I would pull the bullets, dump the powder and get a bright light and look in the case. I've had berdan primed ammo with no flash hole and a few primers with no anvil either. I'd suspect ammo as the primary cause of FTF.

I would put money on it being the primers. I am using TULA primers in my pistol and get an average 2 - 3% failure rate. be glad when they are gone.

Another possible reason might be dirt. I have a friend that just started reloading. He brought his reloads over for me to look at because they weren't going off. Did every check and measurement and the load was fine. Checked the rifle which looked clean. Dismantled the bolt from the carrier and it was fouled badly. I guess he never took it apart and cleaned it.

The OP stated, "dimpled rounds could not be made to fire". Since in almost all cases of an insufficient firing pin blow, another strike will fire the primer, failure to do so is indicative to me of a dead primer. I would shoot up whatever of that ammo that will fire, and scrap the rest.

Jim