1911popo Posted January 26, 2014 Report Share Posted January 26, 2014 will not load a new round off of the magazine. This is with different Armalite magazines and with the standard buffer and a Slash 10 oz buffer. Ejection is normal. The rifle has approx 175 rounds fired thru it The chamber and the feed ramps required polishing. The only other thing was the gas block was sitting on the barrel shoulder and there were no shims or spacers installed. Any ideas? Thanks Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 26, 2014 Report Share Posted January 26, 2014 Homebuilt, or factory rifle? Quote Link to comment Share on other sites More sharing options...
Rsquared Posted January 26, 2014 Report Share Posted January 26, 2014 ^^^^ Good question. As far as the block being up against the barrel shoulder. I built a 16" carbine using a PRI block. Didn't use any spacers and she runs just fine. But, the PRI blocks seem to have a good size port for collecting the gas, so that might be why? I've never had to polish any of my Armalite chambers. Quote Link to comment Share on other sites More sharing options...
1911popo Posted January 26, 2014 Author Report Share Posted January 26, 2014 The rifle is a complete factory built rifle. The ammunition is factory Winchester, Federal and Hornady with 150 and 168 grain bullets, handloads using Lapua brass with 135, 150 and 168 brain bullets. The BCG is well lubed, the buffer spring has been wiped down with an oily rag. The gas key is on tight and staked and has a clear gas path. The chamber had reamer marks toward the shoulder end of the chamber which polished out fairly easy. The feed ramps cleaned up but still could use some more blending and polishing. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 26, 2014 Report Share Posted January 26, 2014 (edited) Mags, then. It's not picking up the next round. Feed lips damaged in any way? No matter which mags - can you load ONE round in a mag, and have it lock back on the empty mag? If you can, that completely rules out a gas problem. Edited January 26, 2014 by 98Z5V Quote Link to comment Share on other sites More sharing options...
Rsquared Posted January 26, 2014 Report Share Posted January 26, 2014 He said that he used different mags. So it's probably not a mag issue. I'd start by putting the stock buffer back in it and starting over. See exactly what she does. Quote Link to comment Share on other sites More sharing options...
1911popo Posted January 26, 2014 Author Report Share Posted January 26, 2014 (edited) Rifle has been returned to all factory components and still short cycles and doesn't lock the BCG back on an empty mag. The 7 magazines are all brand new Armalite that have not been dropped or abused. Will call Armalite customer service Monday ........... Edited January 26, 2014 by 1911popo Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 26, 2014 Report Share Posted January 26, 2014 and doesn't lock the BCG back on an empty mag. Can you lock the bolt back, by hand? Clearances are okay for that? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted January 26, 2014 Report Share Posted January 26, 2014 He said that he used different mags. So it's probably not a mag issue. Don't you get all testy, thinking that an Armalite mag couldn't be the problem... <lmao> Quote Link to comment Share on other sites More sharing options...
Rsquared Posted January 26, 2014 Report Share Posted January 26, 2014 No, no, noooooo. No testiness here. I'll never say that anything that's man-made can't malfunction. Quote Link to comment Share on other sites More sharing options...
Sisco Posted February 4, 2014 Report Share Posted February 4, 2014 (edited) 1911 popo, that fix still working for you? Edited February 4, 2014 by Siscowet Quote Link to comment Share on other sites More sharing options...
1911popo Posted February 4, 2014 Author Report Share Posted February 4, 2014 We finally dis-assembled the gas system and all the components looked good to go. The gas orifice in the barrel was factory drilled at .081 inches. We drilled the gas orifice to .084 and the loaded a 10 round mag with mixed manufacturer known good ammo that ran in another AR10 we had at the shop. The rifle cycled 6 of 10 rounds. The gas orifice was then drilled out to .093 and the rifle ran anything we tried in it including some knwn low powered Mil-Surp. The rifle is assembled with a 10oz Slash buffer and a super lubed BCG and bolt assembly. I'm having to wait for the weather to break for some actual range testing. I'll post the result when I get to go. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted February 4, 2014 Report Share Posted February 4, 2014 Good modification, man - awesome work. <thumbsup> Quote Link to comment Share on other sites More sharing options...
survivalshop Posted February 4, 2014 Report Share Posted February 4, 2014 Kinda makes you wonder ? Opening up the gas port is not always the first thing I would do , with out checking other things first , like sending it back to Armilite , but what ever works . <dontknow> I only had to do a gas port change on one rifle & that was a 10 1/2 " barreled replica XM 177 select fire rifle I built & it made the rifle sing on full auto with out missing a beat . Quote Link to comment Share on other sites More sharing options...
1911popo Posted February 5, 2014 Author Report Share Posted February 5, 2014 (edited) Well the gunsmith at our store is a Marine Corps certified AR 15 armorer with about 40 years experience and I'm a retired mechainical engineer that is also a certifed AR 15 armorer by several of the companies whose products we sell at the same store. As I stated in my above posts we tried and checked all areas, magazines, components etc., etc., for problems. We had gone thru all of the questionable areas such as component clearance and fit up, 7 different magazines while trying all sorts of ammo combinations. The gas key was torqued to spec and the gas path clear and un-obstructed. All that was left was the gas system was not getting enough gas pressure to cycle the action. When the gas system was torn down, the main issue that was found was the undersize .81 inch gas orifice diameter in the barrel. Armalite specs are .084 minimum diameter. When the gas orifice diameter was drilled out to .084 inches the rifle run 6 of 10 rounds without short cycling. I made the decision to open up the diameter to .093 and the gun will run with all types of ammo. In the scheme of things, opening up the gas port was the last thing that was done to modify the rifle so it would function. I would think that we followed an extremely logical approach to find and correct the issue with out undue cost and with a minimum amount time and BS. Edited February 5, 2014 by 1911popo Quote Link to comment Share on other sites More sharing options...
Sisco Posted February 5, 2014 Report Share Posted February 5, 2014 Well the gunsmith at our store is a Marine Core certified AR 15 armorer with about 40 years experience and I'm a retired mechainical engineer that is also a certifed armorer by several of the companies whose products we sell at the same store. As I stated in my above posts we tried and checked all areas, magazines, components etc., etc., for problems. We had gone thru all of the questionable areas such as component clearance and fit up, 7 different magazines while trying all sorts of ammo combinations. The gas key was torqued to spec and the gas path clear and un-obstructed. All that was left was the gas system was not getting enough gas pressure to cycle the action. When the gas system was torn down, the main issue that was found was the undersize .81 inch gas orifice diameter in the barrel. Armalite specs are .084 minimum diameter. When the gas orifice diameter was drilled out to .084 inches the rifle run 6 of 10 rounds without short cycling. I made the decision to open up the diameter to .093 and the gun will run with all types of ammo. In the scheme of things, opening up the gas port was the last thing that was done to modify the rifle so it would function. I would think that we followed an extremely logical approach to find and correct the issue with out undue cost and with a minimum amount time and BS. Having followed you with this issue,1911, I am impressed with how you developed a solution to the problem. Armalite customer service was an option, but you can't argue with success. Nice job, now enjoy that AR10. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted February 5, 2014 Report Share Posted February 5, 2014 Went after a gas-operated 9mm AR like that. Can't remember the manufacturer, but it was high end stuff - it just wouldn't run worth a damn. Swapped the H3 buffer for a standard carbine buffer, and it still wouldn't run worth $hit. Went immediately after the gas port. I can't exactly remember what it was, but it was around 0.060". Went up once, and it ran most of the time. Went up again, I think to 0.083", and it ran like a Singer sewing machine. With the H3 buffer. Shortly after that episode, I started measuring and recording all the gas port sizes on everything I built. If there were ever any problems down the road, I had that info to refer to. Quote Link to comment Share on other sites More sharing options...
1911popo Posted February 5, 2014 Author Report Share Posted February 5, 2014 (edited) In talking with my gunsmith he related this is the first time in all of his experience that he has ever encountered an undersized gas port. His unit rebuilt bunches of shipping containers full of Viet Nam era AR 15 battlefield pick up rifles for upgrades to latest configuration specs. The only short cycling and failure of the BCG to lock back on an empty mag that we both have seen had to do with really dirty weapons, bad ammo, loose gas keys and bad magazines. Oh well........ now if the current modern ice age that we all are now faced with (caused by global warming), would get the hell out of here and warm up so enjoyable trips to range could be had by all. Edited February 5, 2014 by 1911popo Quote Link to comment Share on other sites More sharing options...
Dane Armory Posted February 5, 2014 Report Share Posted February 5, 2014 [quote name="98Z5V" post="90128" timestamp="13 Shortly after that episode, I started measuring and recording all the gas port sizes on everything I built. If there were ever any problems down the road, I had that info to refer to. Quote Link to comment Share on other sites More sharing options...
planeflyer21 Posted February 5, 2014 Report Share Posted February 5, 2014 One of the Brownell's Gunsmith Kinks books has a chart for gas-port sizes for a given caliber, for Remington 74/740/7400 series rifles. That may be a good one to do for the ARs also. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted February 5, 2014 Report Share Posted February 5, 2014 Would be a good sticky to have port sizes of various calibers . I don't have the proper tooling to measure gas ports & for good reason, it doesn't happen that often , but with the increase in the production because of demand , mass produced components may show more imperfections . We can blame it on O' butt head & the surge in demand. Quote Link to comment Share on other sites More sharing options...
Dane Armory Posted February 5, 2014 Report Share Posted February 5, 2014 I have a chart for a lot of calibers But I'm not sharing it this time. It has ranges of gas port sizes for different lenght barrels per caliber and what different manufactors are using. Its like a "Rudder" that the Captain would keep...Trade secrets. Quote Link to comment Share on other sites More sharing options...
1911popo Posted February 5, 2014 Author Report Share Posted February 5, 2014 Drilling a barrel to enlarge the gas port could be a trickey thing to do if the drill isn't sharp or on a stainless steel barrel, not having a good set up to hold the barrel and uppper assembly or just a plain lack of experience of machining. Some things are best left to those who do this for a living I have some information about gas port diameter and location but I would use it only as a guideline rather than hard cold data. I don't want to give away anone's trade secrets or make anyone mad, but some information is better than guessing. A call to the customer service arm of most gun companies can and will get information for your specific firearm. IMHO the easy way to check small diameters is to use small hole drills from a "Numbered Drill Index" and a "Lettered Drill Index". Most of these will get you within a .001 or so. Quote Link to comment Share on other sites More sharing options...
1911popo Posted February 5, 2014 Author Report Share Posted February 5, 2014 (edited) OOOPS BIG FAT FINGERS DOUBLE TAPPED THE SUBMIT BUTTON.................CAN SOME ONE DELETE ONE OF THESE POST? ???? THANKS 1911popo Drilling a barrel to enlarge the gas port could be a trickey thing to do if the drill isn't sharp or on a stainless steel barrel, not having a good set up to hold the barrel and uppper assembly or just a plain lack of experience of machining. Some things are best left to those who do this for a living I have some information about gas port diameter and location but I would use it only as a guideline rather than hard cold data. I don't want to give away anone's trade secrets or make anyone mad, but some information is better than guessing. A call to the customer service arm of most gun companies can and will get information for your specific firearm. IMHO the easy way to check small diameters is to use small hole drills from a "Numbered Drill Index" and a "Lettered Drill Index". Most of these will get you within a .001 or so. Edited February 5, 2014 by 1911popo Quote Link to comment Share on other sites More sharing options...
unforgiven Posted February 5, 2014 Report Share Posted February 5, 2014 Good info brother. <thumbsup> Quote Link to comment Share on other sites More sharing options...
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