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Posted: 5/5/2007 8:45:58 AM EDT
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All wise and knowing arfcom please help my short stroking problems. At least I think it is short stroking. I recently built an A4gery and decided to take it and the trusty ole M4gery to the range this morning and had a major problem with my new build. After a couple of mags on the carbine I decide to try out the A4gery. I had a new mag that I inserted and let the bolt fly on. Pulled the trigger and bang, aimed, squeezed the trigger and click. I thought that I had a mag problem so I pulled the charging handle and it looked like it didn't strip the next round off so I let the bolt fly again. Squeezed the trigger and bang, aimed, squeezed the trigger and click. I decided to insert a mag that I know works and the same thing happened. So I had an empty mag and put one round in it. Fired the rifle and the bolt did not stay open after that round. I am assuming from what little bit about short stroking, that this is my problem. I was shooting Georgia Arms Canned Heat which has always cycled perfectly in my carbine. Could it possibly be the ammo being under powered for a 20" rifle? The rifle was built using a J&T 20" rifle kit. Any suggestions on what I can try to solve this problem. Is it a short stroke problem? Should I have put more than just the few rounds through it? |
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Start trouble shooting from the gas block working aft: 1) Gas block to barrel gas port alignment. 2) Gas block or FSB gas seepage. 3) Barrel gas port blocked. 4) Gas tube blocked or worn. 5) Carrier key blocked, worn or loose. 6) Gas rings worn, missing, broken. Some other probabilities would be improper buffer weight or spring. |
Sure, I just thought I'd include the most popular:
Is the buffer and spring a standard A2? ETA: Barrel gas port may also be under sized. |
 I guess I should have been smart enough to scratch out the worn part myself  That was my first thought. When I ordered the kit they were out of the buffer and spring for A2's and it was a few weeks until the kit arrived completed. I hope they didn't put the wrong spring and buffer in the kit. Is there a way to tell if it's not for an A2? I guess I could just compare it to my carbines spring and buffer. |
www.ar15.com/forums/topic.html?b=3&f=4&t=326890 You can compare the above posted buffer spring lengths to your spring. As far as buffer weights go, the basic weights are unmarked on the face of the buffer. The heavier buffer weights will be marked accordingly, i.e. the next heavier buffer is the “H” buffer and it should be stamped on the face with a “H”. ETA: I recently received a new buffer spring which was supposed to be a carbine length spring. It never occurred to me to measure the spring, I assumed it was “in-spec” and of the correct length. I installed the spring and was very surprised at the range when I went to chamber a round. The bolt and carrier did not have enough momentum to strip a round from the magazine. Good thing I had my spares kit with me. I quickly removed the spring and compared it to a “known in-spec” carbine spring. My new spring was a good .75” shorter than necessary. Just short enough to cause problems. |
Read my edit to the last post. Did you actually measure the spring? Is it in spec? |
That is the Delta Ring, not gas ring. The gas rigns are on your bolt. Is the rifle properly lubed? |
That is not a gas ring, that is your Delta ring spring. Stand by...... |
ah shit. It's a wonder I can wipe my own butt.It was lubed as I put the rifle together. |
Ok, reading comprehension noted.  crodeo, take the bolt group and charge handle out of your upper. Look at your gas tube sticking inside the receiver. Does it look straight? Try to move it with your finger, as you should have a little bit of side to side movement; this is indicative that you properly aligned the barrel nut, because the teeth on the nut should not be in contact with the tube. I have seen a rifle that was short stroking because the barrel nut was over torqued and putting pressure on the gas tube so the gas tube was coming in at an angle into the receiver, so the carrier key was binding on the tube. Remove the bolt, cam pin, etc, until you have just the carrier. Now, with the charge handle still out, hold the upper muzzle down at 45 degrees. Gently place the carrier into the back of the upper. It SHOULD slide down easily over the gas tube. If it does not, then the carrier key binding and that is your problem. |
Well at this point we have: 1) Ensured you have an “in-spec” A2 buffer spring. 2) And you say you used known serviceable magazines. You also did the 1-round mag check which was good. 3) You say you lubed the rifle, I’m guessing you lubed it correctly. Short of removing the FSB to inspect the gas ports in both the barrel and FSB as well as insuring the FSB is not blocking the barrel gas port I would say: 1) Inspect the gas key. Insure the bolts are tight and correctly staked. Take some break cleaner and spray out the gas tube and gas key. I know you only fired a few rounds but this will verify to us that the gas key and gas tube are free of any obstructions. 2) If all else fails, clean, re-lube adding a little more lube than usual and try shooting it again. |
I am going to snap a pic of the bolt and gas rings. |
Good point with the gas tube alignment, I knew I was over looking something. I need to start keeping track of these threads and compile a written list of discrepancies and corrective actions. |
Your gas rings are more than likely just fine. If they look like the ones in my pic above then they are good to go. It’s a good habit to stagger the gas rings when inserting the bolt into the carrier. Some folks here claim that they have fired their rifle with only one ring installed. I personally have never tried that. But, gas rings that are not staggered can possibly lead to short stroking in a weapon that would normally function, but because the rings are not staggered the other problems with the gas system are now evident or compounded. Do the remainder of the checks as I outlined above. |
| I can place the carrier into the upper and let the carrier go and it will slide into place. If I gently push it I do feel some resistance when the key and tube meet but it pushes into place with no troubles. Maybe I just need to lube it up. I will check your sticky in the maintenance section to make sure I do it right. Is gun scrubber ok to spray in the gaas tube? I don't have any break clean here. |
It is tight but the staking doesn't look the greatest. I think I will try and shoot it again tomorrow after a good cleaning and proper lube job. I'll update what happens. In the mean time if you can think of anything else just holler. Thanks for the help Chris |
| Unfortunately I didn't get over to the range yesterday to try it again. Hopefully during the week I will get over there and post an update. If it still doesn't work I will pull the bolt out of the carbine and try it. I should have thought of that while I was there but I was to busy scratching my head. I don't suppose that mounting the KAC M5 could have messed up the gas tube any could it? |
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