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Posted: 1/10/2010 7:16:15 PM EDT
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This is my first complete build. I have followed all of the directions and help topics on this forum. The issue I have is the placement of the gas block on the barrel and the length that it extends into the upper reciever. The gas block is about 1/32" from the barrel shoulder, like YHM instructions say. I assembled the complete upper and lower without the gas tube (last thing I needed to buy) and the bolt slides inside the upper just fine and all operational checks were OK. How far is the gas tube suppose to extend into the upper? The attached picture shows the final tube assembly.
This is the last issue I have before I am ready to head to the range, so please help. PS I first will get a better scope. The following list are the parts used in this build. Essential Arms M4 Uppers Essential Arms Lower YHM 16" 1:7 flutted barrel cabine length system YHM rifle length FF YHM clamp on gas block Spike's Young match grade chrome BCG Magpul CTR stock Magpul MIAD grip RRA Lpk Magpul LaRue scope mount All painted with khaki camo krylon Thanks http://s817.photobucket.com/albums/zz98/68SS2/firearms/?action=view¤t=126_0590.jpg&newest=1 [http://s817.photobucket.com/albums/zz98/68SS2/firearms/?action=view¤t=126_0590.jpg] |
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You have a 16" carbine barrel ? And a clamp on gas block ? And roll pin ?
If you bought a gas tube for that set up & installed the gas tube correctly , I can not think of a reason it should be wrong ? Unless they shipped you a rifle gas tube ? Does the BCG close 100% ? W/o anyghing rubbing or bottoming out ? God bless Wyr |
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Your photo is not showing up for me,
But in the mean time, pull the gas tube and reinstall it. Could be that you did not set the gas tube deep enough in the gas block and the cross pin instead of going through the tube to retain it, is now in front of the tube (tube not seated correctly, and only about half the way in to the gas block tube channel). As for the gap off the shoulder, that would be the thickness of a front hand guard clip, and you only use such gap if you have removed the guard clip for something like a free float tube. |
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Your photo is not showing up for me, But in the mean time, pull the gas tube and reinstall it. Could be that you did not set the gas tube deep enough in the gas block and the cross pin instead of going through the tube to retain it, is now in front of the tube (tube not seated correctly, and only about half the way in to the gas block tube channel). As for the gap off the shoulder, that would be the thickness of a front hand guard clip, and you only use such gap if you have removed the guard clip for something like a free float tube. I was thinking the AR I assembled from parts , I installed the GB flush against the barrel sholder ? And I pushed the gas tube into the GB , far enough to see daylight through the roll pin hole ? God bless Wyr |
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The pin is definitly through the gas tube hole. I lined up the hole so I could see through it and then installed the pin. The hole for the gas tube in a YHM gas block is a through hole, so I can also see the gas tube being almost flush with end of the gas block. I am trying to clear this issue up before going to the effort of removing my FF YHM handguard, considering I have it just perfectly straight and secure.
Would a better install plan be to loosen the gas block with it still attached to the gas tube, put the BCG in the upper installed correctly, and put the gas block and gas tube up the barrel until the gas tube correctly engages the gas key tube. Then tighten the gas block down and go try it out. Should the gas tube go inside the gas key tube about 1/8"? Does the larger end of the gas tube suppose to lightly snap inside the gas key? Thanks And what is wrong with my picture? I have it hosted on photobucket and followed the instructions on this site. |
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Should the gas tube go inside the gas key tube about 1/8"? Does the larger end of the gas tube suppose to lightly snap inside the gas key? Yes, if you have the tube aligned (tweaked correctly), the end of the tube should enter into the the inside of the key. But, make sure that the gas block is aligned with the barrel gas port first, then tweak the gas tube so it aligns to the key afterwards. Depending on your hand guards, if removable do so, then bend the gas tube over the middle of the barrel to align the tube at the end of line with the key (use the carrier with bolt to check the alignment). And what is wrong with my picture? I have it hosted on photo bucket and followed the instructions on this site.
Go to the photo in your bucket folder, left click the photo that you want to post, then when you have the dictated photo page opened, right click the photo and copy address to the page/photo (control C) from it's properties, then in your post here, post this in your first post with out any spacings between the bracket and img-/img to display the photo. [ i m g ]the address to the photo, or control v to paste it from the Control C copy that you just did[ / i m g ] |
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The BCG bottems out on the gas tube. Without the gas tube, the BCG moves and locks up just fine. There is no binding on the BCG. My tube seems about 1/2" too long. How much difference is there between a carbine gas tube and a midlength tube? Is the gas block installed correctly? If you installed it backwards, it might account for the extra 1/2 inch. I have a model 9383 block on mine and the pin hole goes away from the receiver. |
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The BCG bottems out on the gas tube. Without the gas tube, the BCG moves and locks up just fine. There is no binding on the BCG. My tube seems about 1/2" too long. How much difference is there between a carbine gas tube and a midlength tube? Is the gas block installed correctly? If you installed it backwards, it might account for the extra 1/2 inch. I have a model 9383 block on mine and the pin hole goes away from the receiver. I thought of the GB turned around backwards , but that would mean the gas tube hole was drilled all the way through ? Can not see how this would work ? Gas would want to blow out both front and back ? But I only did this one time . The next rifle I did had a factory installed A2 FSB . The rest have been 100% compleat upper , barrel , BCG , CH assemblies ( some with A2 sights & some w/o sights ) . God bless Wyr |
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The YHM clamp on gas block is drilled all the way through. I thought that it was strange to begin with also. The gas tube pin is furthest away from the receiver (closer to the muzzle end).
I have also tried every combo in order to post a picture, and it still does not work. Does someone have email address that I could send it to or help fix it? Thanks for the continued help. |
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The YHM clamp on gas block is drilled all the way through. I thought that it was strange to begin with also. The gas tube pin is furthest away from the receiver (closer to the muzzle end). This has gone completely over my head ! :-( I am going to need a photo to figure out how that GB works , if the gas tube hole is drilled all the way through ? Only thing I can think of is to take the gas tube out , measure it & post that info ? Maybe your tube was shipped wrong , the wrong length ? God bless wyr |
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The YHM clamp on gas block is drilled all the way through. I thought that it was strange to begin with also. The gas tube pin is furthest away from the receiver (closer to the muzzle end). This has gone completely over my head ! :-( I am going to need a photo to figure out how that GB works , if the gas tube hole is drilled all the way through ? Only thing I can think of is to take the gas tube out , measure it & post that info ? Maybe your tube was shipped wrong , the wrong length ? God bless wyr The YHM gas block is drilled all the way through for the gas tube. It is also drilled on the bottom for the gas port and the sides for the pin. The gas tube is capped at the end and drilled on the bottom to align with the gas port. It is indexed at the correct location in the block by the pin. The gas block being drilled all of the way through is probably for ease in manufacturing mass quanities at a low price (read: drill a hole through a long casting/forging then cut it into smaller pieces). It does not affect operational performance. Here's a link to the YHM gas blocks: YHM Gas Blocks |
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The YHM clamp on gas block is drilled all the way through. I thought that it was strange to begin with also. The gas tube pin is furthest away from the receiver (closer to the muzzle end). This has gone completely over my head ! :-( I am going to need a photo to figure out how that GB works , if the gas tube hole is drilled all the way through ? Only thing I can think of is to take the gas tube out , measure it & post that info ? Maybe your tube was shipped wrong , the wrong length ? God bless wyr The YHM gas block is drilled all the way through for the gas tube. It is also drilled on the bottom for the gas port and the sides for the pin. The gas tube is capped at the end and drilled on the bottom to align with the gas port. It is indexed at the correct location in the block by the pin. The gas block being drilled all of the way through is probably for ease in manufacturing mass quanities at a low price (read: drill a hole through a long casting/forging then cut it into smaller pieces). It does not affect operational performance. Here's a link to the YHM gas blocks: YHM Gas Blocks So , it has a " stopper " in the other end ? :-) So it will not let the gas out ? :-) Now , that makes sense to me . God bless Wyr |
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I'm willing to bet the hole is drilled through for production costs. A clean through hole is a lot cheaper, and easier to produce than a blind hole. Though holes just need deburring, blind holes have to be checked for chips, cleaned out, measured and deburred. Blind holes also require depth measurements, and control, so the drill has to be indexed every time it's setup to run in the machine. With a through hole, you know it's GTG when you change drills because your machine is set to over drill by 1/4" or more, and you can check it by looking. It doesn't sound like much work, but it can be a PITA, and add up when you do a few hundred of them. Blind holes also have a higher rejection rate, so using a through hole reduces their overhead by reducing their rejection rates. As for venting from the through hole, it will block up with carbon deposits soon enough, just like the normal gas block does. It's a tight slip fit on a blind drilled block, but it's not a perfect seal. The carbon builds up after a few shots, and makes it a perfect seal. My guess would be that the YHM block is on backward. If it is backward, the gas port in the block isn't lined up with the barrel port anyway, so check by blowing air into the barrel, and see if you can feel any coming out of the gas tube. Just plug the breach side of the barrel with a cleaning patch (hold it in place, or you will launch it), and use a compressor to pump air into the barrel. |
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As you can see in the attached picture, the gas block is still about 1/2" from where it should be. The Spikes BCG is installed in this picture and the gas tube and gas block were slide up the barrel until gas tube properly engaged the gas key.
What am I doing wrong here? All parts seem to be correct. Thanks for helping a new builder out. http://s817.photobucket.com/albums/zz98/68SS2/?action=view¤t=126_0593.jpg&newest=1] EDIT: WHY CAN I NOT GET THE PHOTOS TO WORK. They are uploaded to photobucket and the link is copied in the correct insert tags. |
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I'm surprised nobody has told you to look down the carrier key yet for something stopping it front entering. Could be that (but normal you don't get a spent primer part from a blown primer down the key until you have fired a few rounds), or could be a defective or bent opening channel on the key as well. |
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Thanks for the pictures. Maybe my key is out of tolarance. The tube is DPMS and the BCG is a Spikes chrome match grade
If I try to force the BCG into the upper far enough into the upper with the current tube, the BCG will get stuck in the upper really tightly. Now that I know the tube is in the correct position, I can look at the key/tube connection. Thanks |
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I throughly cleaned the bolt. There seamed to be a lot of carbon in the key, like it has been fired before, even though I bought it new from Spikes.
I then inserted the loose gas tube into the key and marked how far it went into the key. That distance was 0.297" I also measured the distance from the barrel shoulder to the gas hole, which was 0.360" Can someone tell me if these dimensions are correct? Thanks |
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I then inserted the loose gas tube into the key and marked how far it went into the key. That distance was 0.297" Doesn't seem right. I can stick a gas tube into a gas key almost a full inch. I also measured the distance from the barrel shoulder to the gas hole, which was 0.360" Not really sure what you are talking about here. |
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If the gas tube is suppose to go into the key almost 1 inch, then that has to be my problem. My tube will only go in 0.297inches.
I have 3 different gas tubes and they all insert the same distance, so I presume my issue is with the gas key. Thanks. That helped me a lot. The other measurement was from the muzzle side of the shoulder that the gas block is suppose to seat up against to the center of the gas hole on the barrel. I just wanted to make sure the gas hole was in the correct location in relationship to where the gas block is suppose to be. |
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