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Posted: 10/22/2006 4:46:00 AM EDT
Last week, I finally had the chance to try out a custom built upper assembly. Imagine how I felt when I discovered it was short stroking. The first shot wasn't a problem, but I had to manually load the second and subsequent rounds to shoot.  I put this new upper assembly on two different lower assemblies and got the same problem. I had also essentially swapped upper assemblies (for a while) and didn't have any functionality problems unless using Wolf ammo.  But there was never any short stroking in this temporary "franken rifle" configuration!The next day, I called the company I bought the upper from and was told by the service guy that the chamber had to be cleaned out. This is the first time I heard of a dirty chamber causing short stroking.  I followed his suggestion anyway and payed particular attention to the chamber. But as far as I can tell, all I cleaned out was the residue of the relatively small number rounds I fired while dealing with the short stroking.The only thing that makes my lower assembly "special" is the CAA six position collapsible stock. My upper assembly is configured like this: 20” A3 Gov’t Upper Full-Auto Carrier Tac-Latch Extended/Polished Ramps KNS Tactical Crosshair YHM Gas Block/Flip Front Sight w/Bayo Lug and Sling Loop YHM 2 Piece Rifle Length Four Rail Handguard If I don't have to go through the hassle of sending and waiting for my upper assembly to be fixed and returned, I'd appreciate any suggestions on what else I can do. And no, I can't keep borrowing other people's upper assemblies. But I am aware of some others that I wouldn't mind owning.  Edited to revise title. |
| Test it first. Will it lock back on mag when loading just one round and fireing ? Say it dosen't .. Check the bolt carrier gas key to make sure it is tighten to proper torque specs and staked properly. Also could the gas alignment at the front site housen with the gas tube/ barrel/ front site housen all be set up with each other ... Next is what kinda ammo are you useing. Wolf is notourious for being underpower and can cause short cycleing. As also other domestic ammo and surplus. Quality USGI or Cproducts mags are a must also IMO. Is there any binding when you slide the bolt carrier through the upper ? It should slide freely. Hope I helped get you started in your quest to get your rifle right.Good luck WarDawg |
Let's see if I can answer this in the order you put it in... Nope, the bolt didn't lack back on an empty mag after firing the last round. I'll need to go to the range again to see if the chamber cleaning I did made a difference. The bolt carrier's gas key seems to be on tight with the bolt carrier, but the staking is more like scoring.  However, it's my understanding that this scoring isn't a problem per say.The gas block seems to be tightly in place, but I haven't checked to see if it's misaligned in any way. I never used Wolf ammo in my upper, just American Eagle 223 Rem. Full Metal Jacket Boat-Tail. I'd like to try SS109, but I shouldn't buy it just to overcome a short stroking problem. My USGI and C Products mags have been working fine. I tested them on at least three other AR-15s. The bolt carrier slides freely, thus passing the "45 degree angle drop" test. |
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Since you have a few rounds through the upper, mark the gas block where you currently have it on the barrel, and pull it. The barrel will have a tattoo burn where the gas block channel is aligned with the barrel gas port, and if needed, you can realign the gas block if needed. And ditto with needing to clean the upper out of the box. The bore/chamber has a long-term protective coating (most the time, grease), and needs to be removed before it's taken for a spin. |
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I finally had a chance to take off the YHM gas block and unless my vision has grossly degenerated, it looks like the hole in the gas block is about 1/16" AHEAD of the barrel's gas port. Aren't these holes supposed be vertically lined up? I can't move the gas block any further back since it's flush against the front end cap that the handguards go on. Is it time to send the upper back to the manufacturer or shall I employ the allen wrench again to see if there's something I can adjust? |
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If your saying that the barrel gas port is not evening in the tattoo burn area*, you have problems on you hands. Now if the barrel gas port is just not centered in the burn, but still within the burn circle, then all is fine. * Since the gas block channel is larger than the barrel port, the burnt gun powder will tattoo the open area on the barrel?the block port channel. |
I remeasured where the gas block channel was too far forward; it was actually more like 3/32"  Then it occured to me to see if the handguards (and therefore the front end cap) could be put further back. With the muzzle pointing upwards and the stock on a table, I was able to pull down on the handgaurds. The gas block could now be properly aligned! I test fired the upper with the newly realigned gas block and it performed flawlessly!  I can only guess that the gas block wasn't tightened enough during assembly and it shifted forward during shipping...  Now all I have to do is find the perfect scope, continue my plan for adding M16 parts and bargain hunt for ammo to avoid going bankrupt while improving my aim.
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