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Upper Receiver causing issues?

joe777

joe777

Sergeant of the Hide
Full Member
Minuteman
Mar 7, 2023
127
83
Minnesota
My current build is acting up big time with 62 grain FMJ. It will chamber the round but the BCG has a hard time closing all the way forward. Once chambered it is really hard to pull the charging handle and extract. I have to bash on the CH with a mag to open the bolt.

What I've done so far:
Cleaned barrel chamber/extension
Tried the same 62gr FMJ with another AR, works fine
Swapped lowers, BCG, and CH all separately to eliminate variables
40 and multiple other 55 grain ammo seems to be fine
The barrel that im using with this problematic upper receiver has been ran before with no issues, but with a different handguard and barrel nut. I'm assuming that headspace is fine (terrible thing to assume) because ive ran this barrel/bolt combo before. Currently trying to find my 5.56 no go/go gauges.

I've been messing with this build quite a bit so I can't remember if this upper receiver has given me problems, but i don't know if its even possible for strictly an upper receiver to cause issues like this.

Has anyone had an upper receiver cause problems with certain ammo?
 
More than likely it's a chamber issue. Maybe the throat is a little short, or chamber is out of spec. Of course double check your head space, but it could still pass headspace and have a chamber that is not correct.

Is your ammo from the same manufacturer? Maybe check the 62 grain in a chamber gauge too if you have one to make sure it's not a case issue. Color the case with a sharpie and chamber it, see if anything comes off and is noticeably wrong.
 
Bolt closed successfully on a go gauge and unsuccessfully on a no-go gauge.

I didn't have a sharpie so I lightly coated the cartridge in spray paint, let it dry, and chambered the round. BCG did not fully seat. Was harder to pull CH back than anytime before. Must be a tight chamber? Paint was rubbed off on brass and bullet.

Pics below. Ammo is SAA 62 gr "new."

20231023_172904.jpg
20231023_173112.jpg
20231023_173342.jpg
20231023_173404.jpg
20231023_173419.jpg
 
At this point, I would guess your barrel could have a rough / tight chamber... or the ammo is not sized to spec.

Do you have some fired cases , that you could post pics of ?
 
I haven't fired any of this ammo yet since I noticed right away that the bolt didn't close all the way. I can fire some in a week or two, but other 55 gr ammo that i shot looked fine to me.

I think I jumped the gun here by thinking it was somehow the upper receiver when in reality its probably just a tight chamber.
 
I would imagine paint would stop a round from chambering even in a generous dimensioned military chamber. You should have used something like a Sharpie marker that wouldn't have added thickness.

Headspace has nothing to do with minimum-sized chamber. Who made and chambered the barrel?
 
Paint will be thicker and add dimension to the case for sure. A good coat of spray paint could easily add .002+ depending on the paint and how much you used.

I suggest cleaning your chamber thoroughly now to make sure none of that paint is still in there. Go buy a Sharpie and try again. They are cheap and useful in more ways that writing on a bathroom stall door.

You could contact the manufacturer of the barrel and explain the situation. I'm sure they will take care of it if they are reputable.
 
I'll get a sharpie and try it. But the paint was a pretty thin layer and the chamber/ammo acted the same, just even harder to extract.

I believe the barrel is a 18" KAK barrel mid gas, I took it off a cheap Midway upper that I bought and its fairly obvious that KAK made the upper for them. But at this point I'm blaming the ammo more. This barrel has been accurate and fired 55gr hornady, 55gr win, 55gr fiocchi, 55 or 62gr tula, 62gr pmc, 40gr fiocchi, all without an issue.
 
Where did you get the ammo? Is it factory new, or a reload? You stated that you ran Tula, was the tula steel case? Have you run both 223 and 556 in this barrel?
 
Pull the HG and dbl check its chamber, 556 NATO, 223 wylde or 223 rem.
 
Is there something stuck in the chamber? Check it for a partially stuck case.
 
I have 6 rifles that use either 223 or 556. Every one of them has well over 1/8" from the ogive to the lands, measured against 11 different factory rounds. Maybe a case gauge is in order?
 
OP - this is likely an ammo issue. Whether the shoulders hadn’t been “bumped” far enough back, or the bullet is seated too far out of the case, I’m going with it’s an ammo problem.

What I truly wanted to inform you of is how to extract stuck cases/rounds out of an AR. Banging on the CH with a mag isn’t necessary. Lookup a video or two of “mortaring” an AR, but I’ll do my best to explain below:

Basically, if you’ve got a collapsible stock, you’ll want to make sure it is collapsed all the way down to the shortest position. While keeping your face clear of the muzzle, you’ll unlock the CH, and put rearward pressure on it. At the same time, you’ll raise the rifle up off the ground, and strike that buttstock against the ground. The inertia of the two should get that case/round out of your rifle.

I have had a few instances of cases that have been hyper stuck, and unfortunately, I couldn’t get enough leverage on the CH (I’ve got gorilla sized hands, so grabbing that small ear of the CH wasn’t going well). So I ended up pulling out one of my shoestrings. I tied the ends of it together, formed a loop. I then wrapped the loop around both sides of the CH and was able to pull back on the other end of the loop while smashing the buttstock against the ground. That method worked incredibly well. So much so that I now carry a loop of para cord in my range bag for such adventures.

And yeah, one of those sessions really put one of those CAA “Sniper” stocks to the test! LMAO!! It ended up getting shipped back to them in pieces. To their credit, they sent me a brand new one, but it obviously didn’t stay with me after that.
 
Thanks for the info. I tried the mortaring technique a few times but i was indoors and didn't want to damage stuff. The "mag technique" seems to be working ok.


The chamber is definitely marked 5.56 nato and I looked into the chamber and brushed it out, nothing stuck in there.

Is it possible for some of the problematic ammo to leave brass/bullet shavings/marks in the chamber? I noticed that after a 62gr problem round was jammed in the chamber, the next two 55gr working rounds would hang up a bit, but then cycle fine afterwards. I was loading 2-3 problem rounds on top of a mag of good rounds and then cycling the CH manually 5-6 times.
 
62 gr problematic ammo on right, old oxidized 55 gr on left. Both of these were chambered and the 62gr stuck. It appears that the brass shine is being rubbed off. There is a distinct line at the end of the shiny brass that the crappy dark brass doesnt have.

20231024_131457.jpg
 
I would contact the manufacturer and send them the pic and explain the situation. It probably could be cleaned up my hand with a true 556 reamer for the chamber, but I would let them deal with it.
 
humandrummachine said:
Thanks for the info. I tried the mortaring technique a few times but i was indoors and didn't want to damage stuff. The "mag technique" seems to be working ok.


The chamber is definitely marked 5.56 nato and I looked into the chamber and brushed it out, nothing stuck in there.

Is it possible for some of the problematic ammo to leave brass/bullet shavings/marks in the chamber? I noticed that after a 62gr problem round was jammed in the chamber, the next two 55gr working rounds would hang up a bit, but then cycle fine afterwards. I was loading 2-3 problem rounds on top of a mag of good rounds and then cycling the CH manually 5-6 times.
Click to expand...
If chambered in 556, then it’s the ammo. It sounds like the ammo casings are out of spec, either by manufacturer defect, or they are damaged reloaded cases. If you have calipers you could measure them out.
 
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Okay dude, looking at that pic with the oxidized 55gr and the other 62gr, I would continue with the fact that this is the ammo. If you don't have calipers, get some. You can even do the Harbor Freight 6" deals that are like 8.00. Once you get them, measure this portion of your cases (where I circled in the pic). I've seen this issue a few times now, where cases are not sized adequately throughout the entire case. In fact, I just had it with two recent rifles.

Obviously, the cases are laid down, but they appear to be fairly "even" in their positioning. From this vantage point, it appears the shoulder on the 62gr have been bumped adequately. However, the scraping that's occurring as you get closer to the rim, to me, indicates that the case is getting wider the closer to the rim it gets.

If this is the issue, you're options are much simpler: ditch that 62gr ammo and go with something else that is not that.






Cases.jpg
 
It doesn’t look like you have done so, but it would be worth getting a 5.56 cartridge/case gauge. It won’t tell you anything about your chamber directly. But, it will tell you if the ammo is “in spec.” If the ammo passes the case gauge, but won’t chamber, it’s a chamber issue. If the ammo doesn’t pass the case gauge, it’s an ammo issue…

Something like the following; pick your preferred vendor…

 
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Any chance it is a 223 chamber? 5.56 Nato ammo is tight in some 223 chambers. A Wylde or 5.56 Nato chamber has a more open throat. Also you could have carbon buildup, can you look with a bore scope?
 
I still need to order a chamber/bullet gauge to know for sure, but i believe i have a tight 5.56 chamber... i found a comment on a youtube video on a KAK barrel where a guy says he had a tight chamber due to them using an "old reamer." The comment (below) is from 1 year ago, exactly when i bought this upper.

1701967050115.png


I like this barrel but the other day i was shooting at 100, 200 and 300 yards. The 100/200 yard groups were pretty good but really opened up at 300 yards. Could be my shooting or the heat build up. Maybe time to move on haha.
 
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