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Posted: 3/4/2012 6:35:05 AM EDT
| I have an ar15 upper (11.5 barrel with 5.5 pinned suppressor A1 sights) that I am having a problem with cycling. I have tried changing bolt carrier etc. to try to find a weak link. the only thing I can find is what seems to be a major gas leak between the front sight and barrel. If i spray gunscrubber down the gas tube a very large part comes out between the sight and barrel. is there some kind of sealing process that didn't take place on this upper or is a bad case of mismatched machining? is there anything i can do to take care of the problem? Your help is greatlt appreciated. |
| Unfortunately cannot return it. I guess I may just have to get a barrel assy. to replace the existing on the upper. is it brain science to replace a barrel or is it something that should be able to handle on my own. I am curious about head spacing. is this an issue or not? if it is...is there a tool to set the head spacing? |
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it would be more economical and less brain science to replace the gas block edit sorry missed the pinned 11.5
i see posts on people doing with duct tape 2x4 a cresent wrench and a vise and people who do with upper receiver vice and digital torc wrench. It may be worth checking some local shops to see what they charge if your not to certain you can do it yourself |
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Before wrenching on anything, lets take a step back.
First off, is the FSB attached to the barrel via taper pins? Next, pull the hand guards, and this time, determine if the leak is between the FSB to the barrel, or the gas tube to the barrel. Next, using CLP alone, I want you to clean the chamber with a chamber brush by hand, using only BreakFreeclp as the cleaning agent. From there, run dry patches from the chamber to the muzzle until the patches come out dry. Next, I want to to clean the B/C with CLP only as well, and before putting the B/C back in the upper, spray both the outside and the inside of the B/C CLP, give the B/C a quick single flick, now insert it into the upper, then empty cycle the rifle a few times to migrate the CLP from the bolt, to the migrate the CLP to the upper bearing areas. Also, here when empty cycling the rifle , on the last inch'sish of charging handle pull, does it seen that it's harder then the beginning of the pull or harder (should be the same, and not the last inch back harder). Now load only one factory USA made brass case round into a mag (no steel case, reloaded or import ammo), insert the mag into the rifle well, charge the round and fire it. Did the bolt lock back on the bolt catch? If the bolt locked back, drop in 10 round, then shoot them, and again, confirm that the mag is locking back on the last round out of the mag. If so, load up a mag and shoot it. If say in the first 100 or so rounds, you start having problem again with the last round not locking the bolt back, pull the B/C, spray it inside and outside again with CLP, then remigrate the lube from the B/C back to the upper bearing areas. Bottom line, with CLP being the only cleaner and lube being used, now tell me if the rifle is still having a problem short stroking for 200 rounds. If it does not, then the only thing that I want you to add into cleaning the rifle, will be Sweets to clean the bore alone, then back to CLP to clean the chamber with a chamber brush, and CLP to clean and lube the rest of the rifle. |
| Leak is between block and barrel. Short stroking is not being cause by upper being gummed up. AR is clean and setup as it should be. Bolt does not lock back after single shot due to bolt not having enough rear travel to catch the stop. All bolt and carrier components work flawlessy in other ARs. This would lead me to believe that the gas leak is to excessive to cause a short stroking problem and needing to be sealed up. |
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FSB taper pin installed???
If so, then should not having this problem since the taper on the pins should be pulling the FSB down hard on the top of the barrel to seal off any leakage. So on that note, even though the barrel extension is permanent, you should be able to drive out the taper pins, slide the FSB far enough forward to take a look at the gas port/top of barrel at that section to check for burs, and even take a look at the taper pin channels to make sure that the barrel slot channels where drilled correctly so the pin do pull the FSB downwards when the pins are reinstalled. As for solving the leak as it is now, short of just sending the barrel back, use Red loctite on the heavy side between the FSB and the barrel to form a gasket as you slide the FSB back in place, drive the taper pins back in, give a quick blow down the gas tube flow any loctite in the FSB gas passage/barrel port to the bore (just a mop down the bore to remove any loctite that get in there), then wipe up the extra loctite and let it dry for a day. Yes, you will need to heat up the Loctite to break the bond to get the FSB back off, but is going to take more work to get the barrel extension anyway. |
| loctite would do it or if your pins aren't solid.... If the gasblock is not the right size for the barrel id just chop it off spend a couple bucks on a 2 piece that is the right measurement you shouldn't need any additional sealant if its the right size and properly installed. |
| I reinstalled the gas block with red loctite and am going to give it a try. I'm keeping my fingers crossed hoping this will take care of the problem. If this doesn't take care of it I'll probably have to seek some more professional help. I'll check back after I give it a test fire with the results. |
| The stock I am thinking of is a Colt SP1 stock, buffer, buffer tube, and spring. If I do test firings with an M14 style upper on a lower rec. with an SP1 stock would the stock let the upper cycle and work properly of do I need to use the "car" stock for accurate results? |
| SP1 stocks come in two flavors, rifle or carbine, and I am assuming your's is a rifle. Does it have a R6000 or a R6600 buffer? |
| I believe I have my gas problem solved. The bolt is traveling back to latch open on an empty mag. I do seem to be having another issue though. When my rifle cycles it is leaving the spent case in the rifle above the mag. It is extracting the spent case from the chamber but dropping it in the mag well. I have tried 2 different bolts and the are both doing this. Has anyone run into this? Any good tips on fixing the problem. When I have my standard 20' upper on I have no problem everything works perfect. Is it possible that the shorter gas system is still somehow causing me problems? As a review this an 11.5" upper with the pinned 5.5" suppressor. |
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Two things here,
Pull all the way back on the charging handle and make sure that the face of the bolt is not retracting back past the back of ejection port window. Next, pull the Bolt, and first using a spent case off the extractor, cam the ejector in and out of the bolt face to make sure that the ejector is not binding in the bolt face channel, then go to any hardware store, pick up a #60 O ring for about a dime, then install it on the outside of the extractor spring to add more tension to the extractor to make sure that it's not dropping a case. With the increased tension of the extractor in play, take a good look at some of the rims of the spent causes. If you have a rough chamber, or over gasses, the rims are going to be bent up pretty bad by the extractor, and can pin point the problem down to just more than just a weak extractor spring. |
Thanks Dano. I checked things out and everything seemed to be alright so I went and got an o-ring. The local store didn't have them #'ed the same I got the closest fit. After a few test rounds this morning I would have say she is cycling and expelling cases just like she should. I did see the kits on Brownells sight to fix the problem for $12 but I like the $.69 o-ring from the local hardware store much better. Can't wait to get it out to the range a put a few boxes through just for fun 
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