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9/22/2017 12:11:25 AM
Posted: 9/2/2005 10:31:19 AM EDT
I have issues with my Colt H-bar A2, it gives me a failure to feed. The bolt pushes the cartridge 1/3 into the chamber, at which time the cartridge cocks at an angle and dents the casing, any thoughts? Of course I have tried several flavors of ammo. I live in the Upper Shenandoah Valley of Virginia, is there a good gunsmith in the area? BTW, I have read the FAQ and did not see anything that looked like it fit.

Thanks,

Bud Gordon
Link Posted: 9/2/2005 10:49:11 AM EDT
You need to look in the chamber and see whats is going on in there, either that or stop using 243 ammo
Link Posted: 9/2/2005 12:08:04 PM EDT
Does it do this with known good GI mags?
Link Posted: 9/2/2005 12:54:10 PM EDT
I tried a couple of mags, same issue.
Link Posted: 9/2/2005 6:23:18 PM EDT
Any suggestions for a reputable smith?
Link Posted: 9/2/2005 8:48:07 PM EDT
The dent case is being caused by the bolt grabbing the round at the middle of the case and not behind the rim. If you look at the case, and the jam, you will infact see that the bolt is on top of the case, and the it the bolt wedging across the midle of the case with the tip of the bullet in the feed ramps, and the rim of the case still inside the mag feed lip area.

Either you have a short stroking problem, or the mag/top bullet is not getting back high enough for the bolt to grab the case at the rim as it moves back into the lock position. If the problem is happening with several differant mags, then I would supect that the rifle is short stroking, and this is the problem that you will need to track down and correct.
Link Posted: 9/3/2005 4:23:07 AM EDT

Originally Posted By Dano523:
The dent case is being caused by the bolt grabbing the round at the middle of the case and not behind the rim. If you look at the case, and the jam, you will infact see that the bolt is on top of the case, and the it the bolt wedging across the midle of the case with the tip of the bullet in the feed ramps, and the rim of the case still inside the mag feed lip area.

Either you have a short stroking problem, or the mag/top bullet is not getting back high enough for the bolt to grab the case at the rim as it moves back into the lock position. If the problem is happening with several differant mags, then I would supect that the rifle is short stroking, and this is the problem that you will need to track down and correct.



THAT IS IT!!!

I think you have found the problem at least. I'll start searching on short stroke. Thanks!
Link Posted: 9/3/2005 4:33:45 AM EDT
I found the following in Section V for "short stroke". I guess I didn't know what a short stroke was (stupid user error).

The short stroke check is outlined in the Troubleshooting Checklist Gas tubes (the end that fits into the carrier key) and gas rings are designed to wear out. They should be the first things you check if your rifle starts short stroking assuming that your ammo is good. The next thing to look at is your bolt carrier key screws. Use a wrench and make sure the screws are tight and staked. Make sure the gas tube is properly installed (not upside down) and the gas tube roll pin is present. Staggering your bolt rings does nothing to improve the gas seal, having them aligned will not cause short strokes. ARs shouldn't malfunction due to lack of cleaning with less than 1,000 rounds through them. If your rifle only works "when clean,” the real problem is that it doesn't work "when hot.” Do not enlarge the gas port until you have exhausted all other alternatives.
Link Posted: 9/3/2005 7:26:40 AM EDT
Some more info on short stroking:

Q: What causes short-stroking?
A: It is not necessarily high pressure that causes short stroking but higher pressure at the gas port. In a rifle that may have had the gas port drilled out (or just drilled wrong from the factory), and/or a cartridge with a real slow burning powder, the gas that is received into the gas system is much higher than is needed. This high pressure gas fills the gas chamber much faster, causing it to try and unlock the bolt way too soon. At this point in time the extractor in the bolt is pulling on the rim of the cartridge very hard but can't pull it out of the chamber because the case's grip on the chamber walls hasn't yet subsided. The timing of the whole gas system has been speeded up and now it is wanting to try and extract a case that is to tight to extract. When this happens, some of the momentum of the bolt and carrier is lost because the case didn't easily come out of the chamber. A tell tale sign of this is a deep extractor mark on the inside of the case rim. In a properly functioning rifle, the extractor doesn't actually extract, the case is actually driving the bolt rearward. The extractor just holds the case in the bolt until the ejector gives it a flip. Now that the carrier assembly doesn't have enough inertia to travel all the way to the rear, because the grip of the case in the chamber slowed it down, bingo, you get a short stroke that won't go back far enough to lock open or cycle another round. Many times the bolt will come back just far enough to hook the next cartridge in it's extractor groove and try to feed it into the chamber this way. You will get a big dent in the side of the cartridge along with the failure to feed. Some people who don't understand this timing will then think that the ammo must be under powered or that the carrier is not getting enough gas to it. They then drill out the gas port hole believing that this will get more gas to the carrier to force it rearward harder. It does, but now the bolt is unlocking even faster when the case is under even greater pressure. When this doesn't cure the cycling problems, they are then really confused and will sometimes drill out the gas port again!
Another thing that will contribute to the short stroking is a rough chamber. A mirror finish is not actually necessary in a chamber but it should be smooth and not have any grooves in it from a chipped chamber reamer.
Another reason that some rifles will cycle better than others is that not all chambers are cut to the same width. Military style chambers tend to be a little wider by a few thousandths so that the grip of the case on the chamber walls will break loose a little sooner than a rifle that has a narrower 'match' chamber. Companies that like to use 'tight' chambers to make people think that their rifles will give them better accuracy, will have rifles that are also a little more prone to notice differences in ammo pressure levels. Tight is not always better for accuracy. A cartridge and chamber that match each other perfectly with just the right amount of play will be more accurate than a chamber that is tight on the cartridge.
So if you are experiencing a short stroking problem you need to know what size port you have in your barrel. You also need to try different brands of ammo and see what happens. Overall the M16/AR15 is a very reliable rifle and shouldn't be finicky about different ammo, within reason of course.

Q: Are there other causes of Short Stroking? I have an Extraction Problem, is this related? How can they be fixed?
A: One way to tell if your AR is having an extraction problem is to look at the rim of the extracted cases. On a rifle having a problem, there will be an extractor mark deeply into the rim. It shows that the extractor was trying hard to extract the case but it wouldn't come out. The case from a normally operating rifle will show very little extractor marks. I have seen extractors almost pull the rim off of the case when trying to extract it. If you have a short stroking rifle, here are a few things to look for;
1. If it is a new factory rifle, just shoot it more and keep cleaning off the carrier parts and lubing them. Chances are high that it is just too new and it will take a while for the parts to wear in and become slicker. If you are still having trouble after 200-300 rounds, look for other causes.
2. Check your ammo. Try different ammo. Try your ammo in another rifle. Look for pressure signs, flatter than normal primers, firing pin dents that have been pushed back up, holes in the primer, deep extractor marks, brass that has been extruded into the extractor hole, etc.
3. Check the carrier key for leaks. Look for signs that gas has been blowing out from under the key. Check the bolts for tightness.
4. Check the gas rings. A properly functioning rifle will usually work even with the ring gaps aligned. If your rifle works when they are unaligned, but doesn't when they are aligned, look for something else that is contributing to the problem.
5. Check for things like the gas tube being installed out of alignment in the front gas housing. It is rare but it does happen.
6. Pull the front gas housing off and measure the diameter of the gas port. Also measure the diameter of the barrel also as the size of the hole varies with the barrel diameter.
7. Check to be sure the buffer spring is correct.
8. Check to make sure the hammer is not sticking up too far and catching the firing pin on the carriers way forward.
9. Check the chamber for grooves or ridges left from a damaged chamber reamer. These ridges and grooves cause more grip between the case and the chamber wall.
10. Make sure the bolt and carrier are free to move forward and backward inside the upper receiver and that everything looks like it is aligned. Make sure that the magazine isn't hitting the carrier anywhere either.
Link Posted: 9/3/2005 8:29:08 AM EDT
Wait a minute, my faiure is on initial charging, it is before the rifle is fired. If I am reading right a short stroke is only on extraction, am I right?

If this is the case any new ideas?
Link Posted: 9/3/2005 9:14:06 AM EDT
Have you cleaned and properly lubed the rifle? Specifically, the bolt, bolt gas rings, charging handle? Use Break Free for a lube. Check the Maryland AR15 shooters Site for cleaning and lube info. Hope this helps. Charles.
Link Posted: 9/3/2005 9:33:38 AM EDT

Originally Posted By Bud_Gordon:
Wait a minute, my failure is on initial charging, it is before the rifle is fired.




I tried a couple of mags, same issue.


Are they USGI magazines with good followers? I'd say that as long as the bolt carrier assembly is lubed properly, you have a magazine issue.
Link Posted: 9/3/2005 6:23:53 PM EDT
If the problem is only happening on first round charging, then you have either a mag problem, or mag load problem.

If it's you (in reagards to the mag load problem0, then stop it.
Lock the bolt back on the bolt catch, insert and make sure to fully seat the mag by giving the bottom of the mag a sharp blow up with your palm to comfirm that it's seated, then hit the bolt release to charge the weapon.

If it's the mags problem (read confirmed that the mags are seated correctly, but the top round is not not snapping up against the feed lips as the carrier strokes back over the top round during charging, then it's time to pull the mag apart and clean it. CLP works the best to clean the parts and is a good media for leaving a very thin coat or protection on the metal springs. If a good cleaning and light mag lubing doesn't solve the USGI mag problem, then it's time for some new mag springs.

As for the reason that the mags may only be having problems on the first round charge is when the rifle is fired (self cycles), the buffer striking the back of the receiver extension will dance the top round up to the bottom of the feed lips. During hand charging, there is no such jarring action/effect, and the top round is not being pushed up against the bottom of the feed lips, hence allows the bolt to make it past the rim, and contact/shove the case forward at the middle of the case.
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