Flat primers

[Asmodeus6]

I'll get pics up when I get home.

I just put together a 7.62x39 AR pistol

I have fired it twice with Wolf Military Classic 124gr HP

It is a 7.5" Citadel barrel and Alpha Shooting Sports bolt
(A DPMS lo-pro slick side upper that was a take off from a sportical)
And a used AR 15 carrier

It is somewhat of a slap together gun.

Barrel nut was hand tight, backed off, 25ft/lbs backed off, 35ft/lbs, backed off and then cranked to 35ft/lbs and then the next aligning hole. A superior automotive moly lube was applied to the barrel nut threads, but the registered torque to the next alignment hole was around 45-48ft/lbs. (Dry I'm sure this value would be higher.)

Alignment was good.

A Kies adjustable gas block was installed and the gas shut off for the first shot. (I did not have a gas tube at the time) The round did not eject without some pulling on the charging handle. This is polymer coated steel case ammunition.

When I ejected the round (manually) I inspected it for drag marks, abrasions, deformations and the primer hit. The hit looked good, and the gun went bang so I didn't pay much attention. Next round. Click. (knew this was coming) I was using a standard firing pin, and power spring. eject that manually, set it aside. Hit looks about the same as the one that went bang, so, I face it down range on the bench and let it hang out for a minute or two. Next round. BANG! Really hard to eject again. Like, 15-20 seconds of pulling on the CH with light to moderate force to get it out. (I was not being rough on the charging handle, but it required a series of repetitive pulls to get it out) The next two rounds didn't go bang. So 2 of 5 went bang, and the other 3 did not. I hit the 3 twice, still no bang.

After letting them sit for a few minutes I looked at the primers. The ones that did not go bang, seemed set deeper. But in actuality it is more likely that the two that did go bang flattened out a little from being set deeply like the others. They are not flat enough to cause me great alarm. But being that it's new. And I've shot thousands of rounds of this stuff without issue in AK's...

It was worth getting a second set of eyes on the issue.

Is it possible that I'm getting a little more pressure signs because there is no gas being bled off to cycle the weapon?

Or is it more likely I have a chamber/head space issue that is going to need resolved?

Pics will follow when I get home tonight.

[red dog]

i am thinking you might want to check headspacing just in case. this is always a good idea on a new build, even more so on one built with misc. leftovers.

[ByblosHex]

I dont have much experience in this, but... It sounds almost exactly like what happened to one of my friends with his AR while using reloaded steel cased ammunition. The ammunition was not fitting into the chamber all of the way properly. Maybe the ammunition is deformed or otherwise defective? Try fresh ammo.

[Asmodeus6]

i am thinking you might want to check headspacing just in case. this is always a good idea on a new build, even more so on one built with misc. leftovers.

The barrel and bolt were a new set from the same place. The upper was a known good rec from a factory built rifle (DPMS) I swapped out for a dust cover equipped rec. The lower shouldn't even factor into the equation, but it's a billet unit that functioned flawlessly with my other pistol upper. The bolt carrier was from that 'other' pistol upper, and had about 1600rds on it. It was well maintained and had little to no wear showing. (pistol caliber) Cam pin was a new unit. So there shouldn't have been a worn/mating issue with that either.

I dont have much experience in this, but... It sounds almost exactly like what happened to one of my friends with his AR while using reloaded steel cased ammunition. The ammunition was not fitting into the chamber all of the way properly. Maybe the ammunition is deformed or otherwise defective? Try fresh ammo.

The ammo is of new manufacture. It is not reloads. The FTF is related to using a 5.56 firing pin on hard primer 7.62x39mm ammo. This is a known issue with 7.62x39mm AR15 variants, and there is an extended firing pin out there to solve the issue.

I was aware of that.

I did extensive work on the receiver extension to aid in feeding the much wider 7.62 round as well. Bushmaster does this on an OEM level to aid in feeding. Which is also a known issue with these guns. They mill almost the whole bottom out of the extension. I didn't go quite that far. But I worked on it until manually feeding rounds was no different than a typical 5.56 AR 15 is with a full mag. Manual feeding and extraction of unfired rounds is smooth as butter now.

Initially it was shit.

I left ALL of the back sides of the lugs intact. (in case anyone was wondering.) So the full lock up is still there.

This is after just a light touch up. (It was NOT ENOUGH)



And this is what it took to get rounds to feed reliably without deforming the bullet itself, with gouges from the sharp edges of the lugs.





I have a variety of 7.62x39mm ammo I can try. Including Yugo surplus. But I expected those to be even harder to set off than the Wolf. So I went with Wolf. I have hotshot, Barnaul, Wolf, Chinese, laquer, poly, FMJ, HP etc. Lots of AK mouths to feed here, so I'm not in short supply or variety of 7.62x39mm here. I don't think this is an ammo issue though. It's a gun issue.

Not concerned about the insufficient hits either. Already ordered the ext firing pin. It's been shipped says my email today. (XP hammer spring too JIC)
I'm worried about excessive head space allowing the round to swell. Making it stick in the chamber, and trying to push the primer out the back.

OR - am I seeing higher pressure on the case because no gas is being bled out of the system to work the action? I understand the bolt unlocks under reverse pressure in an AR 15 by the bolt being blown from the back by gas pressure. Could that be why the cases are hard to extract without gas assist? It is a new chamber as well. So it could be a little rough, or tight. But if it was tight, why would I get primer flow? Isn't that normally a too wide of a tolerance?



I have a gas tube on it now. So the next chance I get I'm going to turn the gas 'on' and try to send a few down range. I just wanted to get a second look before I did so. Primer pics when I get home.

[Asmodeus6]

First fired round, unfired Wolf 124gr, unfired Yugo


Second fired round, unfired Wolf 124gr, unfired Yugo


First fired round, second fired round, 3 hit twice but not fired, unfired Wolf 124gr, unfired Yugo



Doesn't seem as bad as it did yesterday. I think I'm just used to AK hits on these primers. Which are typically VERY hit looking and kinda smashed in. I am used to seeing more of the edge of the primer not so flush.


Paranoia?

[red dog]

sounds like this isn,t your first rodeo. seems to me you have done everything right. i would still like to see you check headspace. i do not think you are getting over pressure by not using a gas tube, the barrel is shorter than the gas port on rifles. you can still get over pressure with a bad headspacing issue. are the primers totally flat or just starting and leaving round edges. if the latter it might not be a big deal. i have a savage 308 with such a tight chamber it slightly flattens the primers well below max loads, hell the cases still fit my case gauge i use when loading. even though you got a match set: bolt and barrel it doesn,t automatically guarantee a good headspace. as far as the cases sticking i had the same problem with my 7.63x39 hbar. i started using copper washed and brass cased ammo instead of the poly coated cases, problem fixed.

[Asmodeus6]

Yeah, I'm probably going to invest in some head space gauges. I have enough rifles around here chambered in this caliber it would hardly be a waste.

My concern was the first picture. I've never seen a x39 round flatten and start to flow like that in any AK I have. I've owned all of mine from new through thousands of rounds. AK's hit primers hard, at least mine do. Which usually (if anything) makes it look like the edges are curling away from the case since the pin hit is so deep and wide. I've never seen them flow back towards the bolt face AT ALL, so maybe it's just me being 'new' to x39 in the AR platform. Or there's some kind of dynamic that's different with the bolt face. (Or chamber, or head space.)

Apples to oranges of course. But this is 54R out of a PSL. Which, we all know is an AK graduated to "limousine" status. (And stature)

See how the primers STAY at the installed depth OR are smacked in further after being struck?






My AK's hit like the PSL does. DEEP, wide, and the primers DON'T swell back at the bolt face.

So when I saw these (AR in 7.62x39) primer hits. I figured I would put it before the panel of PAFOA and get some thoughts.

It's certainly not my first rodeo. But it is my first AR in 7.62x39. My last off caliber upper was 7.62x25mm. And I learned how tolerant the AR platform is of other calibers. (Gas operated, not blowback) And what will stuff it up quick and proper if it ain't right. With this I'm limited to ASC conversion mags. So there was no room for working on them like there was the PPS-43 mags. Those I could fit to the conversion block, and adjust height, feed lips... etc. These are paper thin aluminum horse shit. So much to my dismay I fit the gun to the mags. (Hacking open the barrel extension) Which goes against my judgement of always fit the mag to the gun. I took precautionary steps with the adjustable gas block, to avoid beating the crap out of the gun with heavy loads.

Which I plan to shoot. 154gr soft points are my next move after I get things sorted out with the lighter loads.

you can still get over pressure with a bad headspacing issue. are the primers totally flat or just starting and leaving round edges. if the latter it might not be a big deal.

They are not totally flat. But the center portion around the pin is nearly flush with the bolt face. The edges still have some depth, but the center appears almost or nearly flat to the bolt face. It is NOT protruding, even around the pin. It is all below the bottom of the case and still in the pocket. It just seemed abnormal from what I am used to seeing.

Thanks for the responses.

[Lycanthrope]

Measure the length of the fired cases as compared to the unfired. Also measure the OD of the case near the base of both fired and unfired cases.

Tell us the numbers.


Lycanchamberissuemethinksthrope

[Asmodeus6]

Measure the length of the fired cases as compared to the unfired. Also measure the OD of the case near the base of both fired and unfired cases.

Tell us the numbers.


Lycanchamberissuemethinksthrope

Too big, or too small do you think? I don't have digital calipers at the moment - so I'll have to borrow some.

[Lycanthrope]

Could go either way, but I'm leaning toward not enough headspace.

Lycanhardtosaythrope