Newb AR15 ammo question

[71chevellejohn]

Before Christmas, I bought a brand new AR15. One of my good friends bought an identical rifle at the same time.

First time out shooting it, I had no problems that weren't remedied by a quick oiling. I ran probably 80-120 rounds through it of the Federal 556 62gr that I bought in bulk at Academy(bottom shelf in the green ammo can).
After that time out, I broke it down and cleaned/oiled it thoroughly. The next day we took it out again. On this trip, using the same ammo, I don't think I got more than 3 consecutive rounds without it stovepiping on me. We disassembled and checked it out, but couldn't find any cause.
Both times out, my friend had run about the same amount of ammo through his without failure. The only difference I could find was the ammo(he has a large stockpile of ammo he was firing from). Seeing that as the only difference, I went and bought two different brands of ammo from our local range(one is "MFS" and the other is "Hotshot", I believe). Both of the new brands are 55gr instead of the 62gr that the Federal is.
Took it out today and with the Federal, I fired 5 shots with 3 jams. Pulled that magazine, and went through 30 rounds each of the new stuff without failure. Put the Federal back in and had 2 more jams in 5 more shots.

Now for the noob questions: Is 7gr that big of a difference in ammo? Or is that Federal stuff junk? Is the rifle just picky? Is there something else going on that I should look for?

Thanks in advance for any insight or advice you can give.

[LANTIRN]

First you need to make sure you are using the correct ammo. Is your gun 5.56 or .223, or .223/5.56? .223 and 5.56 are NOT the same ammo. Second, if it has a direct impengment system and not a piston it is going to have problems. 6 years in the Air Force and every time we would shoot the M16 (with DI) about half the guns would have problems (and they were cleaned every time they were shot). This is why mine has a piston on it.

Also, and most importantly, you did not specify brand of AR or brand of mags. If you are using Pro Mags, they will cause problems. As far as specific problems to AR brands, I am not the guy to ask; maybe CJ will chime in.

But please, do not shoot 5.56 ammo in a gun chambered for .223. If you bought it at Academy I doubt it as 5.56 but you never know.

Also, if you shoot brass then steal, you will probably be fine, but if you shoot steal then brass it will cause jamming issues.

That is all I can think of for now. After I get another drink I will see if anything else pops into my head.

[Roger]

Any chance it's a bad mag or are you having trouble with that ammo in all the mags?

[Sleeper]

I've never seen a picky ar.

[Reefer Rae]

My cheap ass dpms eats Winchester and shits wolf , 2000 rounds plus . Cleaned it once last April . It will shoot anything . I'm trying to find the failure point and haven't got there yet .

[helosailor]

I'm going to take a shot and say that it is probably a magazine issue. Are they the magazines that came with the rifle? Do they have a brand stamped on the bottom? I have run Magpul Pmags almost exclusively with mine, with all different kinds of ammo and have not ever had a failure of any kind with various ammo from 40gr up to 69gr. I have probably 1000 rounds total through it.
Another thing to look at is the extractor. Some cheaper made rifles/bolts have less than excellent extractors.

[Trick Pony]

I always shoot the cheap Federal American Eagle and Remington UMC .223 ammo from
Cabela's and have never had any failures in the gun I built with the
Surplus Arms & Ammo lower and Daniel Defense upper AR that I built with no failures.

[Skidmark]

Next time out, trade mags with your buddy to test.

[likeitfast55]

There always seems to be a lot of confusion over the difference between a .223 and a 5.56 chamber. Is it safe to shoot this? Is it safe to do that? More confusion is added when some manufacturers advertise rifles with .223/5.56 chambers. I found this 'excellent' explaination on Wikipedia (http://en.wikipedia.org/wiki/.223_Remington) and wanted to share it on this forum.

"The .223 Remington is a sporting cartridge with the same external dimensions as the 5.56x45mm NATO military cartridge. It is loaded with a .224" diameter, jacketed bullet, with weights ranging from 40 up to 90 grains, though the most common loadings by far are 55 grains.

The primary difference between .223 Remington and 5.56 x 45 mm is that .223 is loaded to lower pressures and velocities compared to 5.56 mm. .223 Remington ammunition can be safely fired in a 5.56 mm chambered gun, but the reverse can be an unsafe combination. The additional pressure created by 5.56 mm ammo will frequently cause over-pressure problems such as difficult extraction, flowing brass, or popped primers, but in extreme cases, could damage or destroy the rifle. Chambers cut to .223 Remington specifications have a shorter leade (throat) area as well as slightly shorter headspace dimensions compared to 5.56 mm "military" chamber specs, which contributes to the pressure issues.

While the 5.56 mm and .223 cartridges are very similar, they are not identical. Military cases are made from thicker brass than commercial cases, which reduces the powder capacity (an important consideration for handloaders), and the NATO specification allows a higher chamber pressure. Test barrels made for 5.56mm NATO measure chamber pressure at the case mouth, as opposed to the SAAMI location. This difference accounts for upwards of 20,000+ psi difference in pressure measurements. That means that advertised pressure of 58,000 psi for 5.56mm NATO, is around 78,000 psi tested in .223 Rem test barrels (SAAMI .223 Rem Proof MAP is 78,500 psi so every 5.56mm round fired is a proof load, very dangerous). The 5.56 mm chambering, known as a NATO or mil-spec chambers, have a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 chambering, known as the "SAAMI chamber", is allowed to have a shorter leade, and is only required to be proof tested to the lower SAAMI chamber pressure. To address these issues, various proprietary chambers exist, such as the Wylde chamber[2] or the Armalite chamber, which are designed to handle both 5.56 mm and .223 equally well.

Using commercial .223 cartridges in a 5.56-chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223-chambered gun due to the excessive leade. [3] Using 5.56 mil-spec cartridges (such as the M855) in a .223-chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and the SAAMI recommends against the practice.[4] Some commercial rifles marked as ".223 Remington" are in fact suited for 5.56 mm, such as many commercial AR-15 variants and the Ruger Mini-14, but the manufacturer should always be consulted to verify that this is acceptable before attempting it, and signs of excessive pressure (such as flattening or gas staining of the primers) should be looked for in the initial testing with 5.56 mm ammunition."


I copied and pasted that article from another forum. It seemed very clear and explanatory on the subject.

Randy

[Fatass]

Buy pmags. I'll put money on it being a cheap mag/junk follower. DI has worked for how many years? Oh, right.

[soap]

I also think it's the magazine. Few months ago my brand new AR. Jammed on the 2nd round... then I broke out the P-MAGS. 500 rounds never jammed again.

P mags. FTW

[71chevellejohn]

Thanks for the responses!
I don't think it's a mag issue - it came with a new 20 round generic magazine. And one of my buddies in the Army brought me some used freebie mags. I also bought 3 brand new Magpul Pmags. The problem occurred with each variety of magazine. A magazine problem was my first thought. But when I thought about it, it seems that the spent casing isn't being ejected quick enough.

I'm thinking the ammo is the key... the Federal I bought from academy is marked 556 and the two different brands I used earlier are both 223. i'll check with my friend and see what his ammo is - and see what happens when he runs my Federal through his rifle.

The rifle is a Del-Ton upper and lower. I don't/didn't see any indication whether it's 223 only at the show. I'll send them an inquiry about that. That may also be the root of the problem.

[Sleeper]

I'd really check for gas leaks. Does it lock the bolt back on the last round?
Also look at the extractor and see if anything is weird.

Check all bolts and make sure they are tight. Any obstruction in the gas tube. Really look it over well.

Ar15s are a simple rifle.