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1/25/2018 7:38:29 AM
Posted: 11/26/2002 4:56:02 AM EST
Hi guys, I'm new to the site, but I've been shooting AR's since the 60's. I have a problem with my FN barrl/upper that I can't figger out. If you shoot at between 60 and 90 rounds through it rapidly (aimed, not crazy) it will start to have extraction problems. Cases get stuck so bad that you have to hit the charging handle to extract them. The extractor doesn't usually don't go over the rim.

I looked at the chamber, it's chrome plated, and smooth as can be with no rings or scratches. I have tried lots of different kinds of ammo, including mil-spec..I have tried different mags and extractors, but no luck. I have scrubbed the chamber until I'm blue in the face, and tried it bone dry. A Class III friend shoots hundreds thru his at a sitting, but he says he lubes all his cases with CLP, but I don't wanna do that. I tried it, but it didn't help much. Any suggestions...??

P.S..none of my other AR's do this, so I don't think I'm causing it myself.

Thanks, greco
Link Posted: 11/26/2002 2:28:21 PM EST
[Last Edit: 11/26/2002 2:29:37 PM EST by Dano523]
Most of the time when a case sticks in the camber, it is signs of over pressure. This can be caused by; 1. The round being loaded too hot. 2.The wrong ammo being used in the rifle, such as using 5.56 in a tighter 223 REM chamber. 3.The throat of the chamber being reamed too short and the bullet imbedding into the rifling, causing the round to overpressure before the bullet starts to move. Since you have left out the make of the rifle, ,the barrel type and chamber spec, you will need to give us a little more info to help you trouble shoot the rifle. Also, check the barrel for what type of chamber was cut. The barrel should read 5.56 or 223. Although most people believe that the two are the same, the 223 chamber is tighter and the throat shorter than the NATO chamber. Also, you don't need to spray CLP on the cases, but the bearing surfaces of the upper should be kept a little wet with with CLP. It aids the rifle in break in, and keeps the rifle running, due to fouling.
Link Posted: 11/27/2002 4:23:01 AM EST
Greco said it was an FN barrel. I do not know if FN builds anything but GI barrels. Being as they are the current M16 supplier, that is what I would expect. I agree that it sounds like excess pressure. Look over your empties for: Pierced or cratered primers; missing primers; brass extruded back into the ejector plunger hole. If you have a micrometer, check the diameter of the head (just above the extraction groove) before and after firing (growth should be less than 0.0003") and tell us that change. Any of these says a too much pressure. If the ammo works in other rifles, it implies a "small" chamber, as Dano523 described.
Link Posted: 11/27/2002 5:36:51 AM EST
Well fellas, I grabbed a st of mikes and some fired and unfired cases that went through this carbine (16"). Unfired cases read .375, while fired cases read the same...hmmmmm. The necks are .248 to .250 on unfired ammo, and .254 on fired brass...hmm. There is no primer protrusion, they are not flattened, the edges are nice and round like they should be, no flow or cratering....I looked for that cause I've been handloading for 30 years. The barrel has absolutely no markings that I can see with the handguards off. It's a nice piece of work......heavy heavy, untill it bumps out to .975 near the chamber. Now that you mentioned it, there are no markings on the upper either..?!?! It is nicely made inside and out, except that the casting flashings haven't been smoothed real well...but I haven't too many that are. My Colt's are about the same. Hmm..I hope that's enough info to get your much needed assistance. I have already had this thing checked for head space.....thanks again..da greco
Link Posted: 11/27/2002 9:16:00 AM EST
Me again.... I remiked the fired cases.it looks like unfired they're about.374, they read .375 to .376 when fired. Is this too much ?? g
Link Posted: 11/30/2002 10:14:33 AM EST
Well....I got it fixed the easy way.bought a new Colt upper assy.looks good too. thanx greco
Link Posted: 12/1/2002 8:39:14 AM EST
Hey Greco, have you polished the chamber yet. I am a real believer in polished chambers on all autoloading rifles. Flitz on a mop, 220 wet-or-dry on a slit dowel, whatever works. Chambers should be slick or they do tend to hang up.
Link Posted: 12/1/2002 1:51:34 PM EST
yep, I had already Flitzed the chamber....and it was like a mirror. I just think it is out of spec...someone mentioned that FN stuff does get out to the public. It may have been a reject that Sherluk sold me. I went to the range today with the new upper (and same bolt/carrier). Ten thirty round mags without a burp, all mixed types of ammo. Just the way it should be. I guess I will stick with the better vendors and better known quality parts from now on. I guess it's true, ya get what ya pay for. But I still got a real real nice AR for about $650-700 invested. Now that I know that the thing works, the next trick may be to put a scope on it. I have scopess on the other AR's (all Colt uppers by the way--with no problems ever). I usually wring my stuff out hard when it's new because I wanna make sure it will really work when I need it to work. I wouldn't have known the other upper didn't work reliably if I had just shot a couple of boxes through it at a time like some folks do. But now I can shoot just a few here and there because I gave a good wringing out. On a side note...the guy at Sherluk who sold me this defective upper at Knob Creek now sells AR parts under the name Tony's guns, or something like that (Tony something). This Saturday I saw him at the Birch Run show in Michigan. He looked at the upper and said he never sold me that upper. But I know it was him because I have seen him at the Knob and at gun shows for at least 10 years. Now it makes me suspicious of the spare parts I have bought from him over the years..like bolts and carriers, and other stuff for an AR. I hope it wasn't ALL rejects. Thank you all for your help.
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