AR Sponsor
Posted: 1/17/2005 2:52:02 PM EDT
|
I have a problem with a model 1 upper and can't figure out how to fix it. This upper worked fine for the first 1,000 rounds and now it will not extract the empty rounds. At first I thought it was due to a weak extractor spring so I changed that and it still will not extract. I know the chamber is not tight because you can tip the barrel up and the empty will just fall out on it's own. I tried taking a complete bolt and carrier off a Bushmaster that I know works and it has the same problem. If you have a full mag the bolt will come all the way back and try to chamber a fresh round which will cause the new round to jam up under the empty because the empty casing is still in the chamber. If you put only one round in a mag the bolt will hold open which tells me the gas tube is just fine but it still will not extract. When I first got this upper I noticed the lugs on the bolt would drag against the lugs on the barrel (is this called the barrel extension?) but the strength of the recoil spring was strong enough to overcome the drag and lock the bolt in battery. My Bushmaster bolt drags against the barrel lugs as well. I think this drag is causing the extractor to lose it's tension or grip on the empty casing which will not allow it to extract. Is it possible for the barrel extension to be rotated or out of alignment? Any thoughts would be greatly appreciated as it is driving me crazy and I have got to get this fixed. Thanks, MadDog 
|
|
The carrier key is tight on both the Model 1 carrier and the carrier from my Bushmaster. I have the same problem with a new bolt and carrier from my bushmaster that I am positive works 100% in other AR's, just not in this Model 1 Sales upper. The bolt locks back every time on the last round, it just will not extract the empty casing. This tells me there is nothing wrong with the carrier key or gas tube. The only difference between the Model 1 upper and all my others is that the lugs on the bolt drags on the side of the lugs on the barrel. I get this drag of the lugs on every bolt I try. None of my other AR's do this leading me to believe the lugs on the barrel are undersized or not aligned properly causing the extractor to hold open a little and not grip the casing with the proper amount of tension. I am going to try the #60 O-Ring trick and see if that helps. MadDog 
|
|
Have you replaced the extractor? or placed a spent cartridge in the bolt face to s if the rim engages the extractor at all. If the extractor checks out you need to check for excessive head space. if the chamber is too deep the extracter never has the chance to grab the case rim. Have you tried the M1 bolt/extractor in the bushy? This will eliminate te bolt/extractor or point it out. Good luck. |
|
Fixed My Problem!!!! 1) I tried replacing the extractor spring with no luck. 2) I tried switching out bolt and carrier with one from another rifle that I know works with no luck. 3) I tried the O-Ring trick on the extractor with no luck. Talked to a friend who asked me if I had used any oil in the chamber at all. I told him that the bolt lug to barrel extension fit was very tight and that I used quite a bit of Firepower FP10 on the lugs. He said I probably got some oil in the chamber and that it was causing Vacuum Pressure which was keeping the fired casings from extracting. I cleaned out the chamber and barrel extension with some Gun Scrubber and low and behold the problem is fixed. Just took it to the range and ran 200 rounds "rapid fire" (as fast as I could shoot) through it with zero malfunctions. Problem solved, MadDog 
|
|
tagged to read in its entirity later... meanwhile, I'm facing same problem in this thread |
Really frightening the depth of knowledge your friend displays. Your chamber goes from 45,000 psi to vaccum pressure in those milliseconds prior to extracting the case due to oil in the chamber  Maybe just cleaning the chamber did the trick. Sure would make more sense from a scientific viewpoint. |
I was having problems with that explanation as well, but hey, what the hell do I know. I couldn't see a vacuum being created with a .223 sized hole existing at the end of the barrel. It works now, so who cares, I guess. |
|
centauro97 Call it vacuum pressure or whatever you want, but i just did a very un-scientific test and my friend was correct. Like you, I thought it was just a coincidence that cleaning out the oil worked, so this evening I lubed up the chamber with some FP10 and went back out to the range. Guess what??? Massive extraction failures. Cleaned out the chamber again with Gun Scrubber and guess what? Put another 150 rounds through it with zero failures. This thing runs like a Swiss watch with a dry chamber. MadDog 
|
Uh, DUH? You don't lube the chamber, bore, or ammo before firing. Bore and chamber should be clean and dry before firing a shot. Has nothing to do with "vacuum pressure" (whatever the hell that means) has everything to do with changing the chamber dimensions and increasing chamber pressure. Might I suggest you buy a copy of Hatcher's Notebook? This is covered in detail. |
|
Who is Hatcher and where might I find his handbook? Also, vacuum is probably not the right term... I'm thinking 'stiction' or 'surface tension' or 'adhesion' might be better terms.... As the case expands it expels any air between it and the chamber... which has a thin film of oil. Then the two peices of metal are semi-bonded by that oil layer. You can recreate this... find two small strips of metal with smooth faces, oil one, stick the other strip to it. If this is the cause of my problem I'm going to scream! I don't "store" my weapons, I keep them fire-ready. That means I dont lube the bore/chamber - so I dont have to dry-patch them before firing. Having said that, I do run a bore-snake thru with CLP on the front two inches prior to putting it away. I also am generious with CLP on the bolt, I like my rifles wet. I stow my rifle by hanging it muzzle-down with a muzzlecap, bolt closed and hammer dropped. I suppose its possible that CLP from the bolt is pooling in/around the chamber, and because I do not make a practice of dry-patching before firing ("excuse me Mr Home Invader while I dry patch my bore"), this may be causing me problems too. But why does it seem to be restricted to Model1 uppers? Shaw barrels have an odd chamber? Oh well, I have some bolt parts and headspace gauges on their way from Brownells anyway. Useful to have on hand I guess. :) |
That sounds more plausible than vacuum. I wasn't denying the issue, but the vacuum theory didn't fit.................................................so you must acquit. 
|
|
On the whole, chrome barrels are more 'slick' (for lack of a better word) than plain steel barrels. I do not see how your sticking problem can be from a vacuum; when a case is ejected, the chamber still has plenty of pressure in it, but at safe enough levels to extract the case without danger. Your sticking problem may be from the oil's surface tension, and its lack of its ability to part (seperate) rapidly. That is one property oil is supposed to do: keep a constant film. I really believe that if you keep you chamber very lightly oiled, you should be fine. With my match barrels, I coat the bore and chamber with moly oil from Midway (made by KG Products); then, run a dry patch through to remove the excess. I have never had an extraction or chambering problem. In my non-match barrels, I use Ed's Red: which can be found here. |
|
I am sorry I used the word "vacuum pressure" as everyone seems to be hung up on that word. Call it what ever you like. The bottom line is, I have extraction problems with a NON chrome lined barrel if there is any oil or lube at all in the "chamber". If the chamber (not the bore) is dry the upper runs 100%. I do not have any problems with my other uppers that ARE chrome lined even if there is a substantial amount of lube in the chamber. MadDog
|
|
I'll be going to the range Friday to test this all out.... as for Ed's Red, I made up several gallons of the stuff a few weeks ago and it is THE SHIT! It softens carbon well so that it can be removed easily. Instead of only CLP (and Hoppes9 on my antique's), I'm adding Ed's Red to my cleaning regimen. |
MadDogMan: Can you do a cast (rubber or metal) of your chamber? Or, can you borescope it? Is there a possibility that your chamber has machine marks that somehow effect extraction with oil? I am running out of ideas on what is causing your problem. But then again, it if shoots with a dry chamber and groups well: go for it. I have a match rifle that is finicky (spelling?) as heck. It will ONLY group Sierra 168 grain Match King bullets with moly. Thus, I ONLY shoot these bullets in my match rifles. I figured doing this was easier than trying to keep different bullets for every rifle. |
AR Sponsor