1911popo

OK Thanks, Dave

Thanks, Dave

Ok I'll play 20" AR 10 T HB .096 diameter 16" 5.56 Noveske HB .084 diameter 24" 5.56 Krieger HB .089 diameter

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.

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.

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.

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.

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.

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 ...........

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.

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