Originally posted by explorecaves
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how to hold upper reciever?
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Originally posted by LRRPF52 View PostThere's no way to see where the gas tube holes are aligned unless grossly out of place looking through the rear of the receiver. If you barrel nut is like most of them on the market, you really need a way to see from a dead-on front perspective to align the teeth or hole and gas tube hole on the upper.
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When you start to look at gas tube alignment inside the upper receiver when going through your trouble-shooting stage with a stripped Bolt Carrier, it can make a huge difference.
I disassembled my 16" Grendel just to check the squareness of the face, and reassembled it. As I was installing the gas block with tube attached, I wanted to see if I could just mount the rear of the block flush with the shoulder on the barrel profile step, so I determined my gas port locations, and found that I could.
Once I got the block positioned (it's a JP that I modified), I went to check my Bolt Carrier interface with the gas tube, ensuring that there was no binding. I clamped it down, and re-tested the BCG, which promptly got hung up from coming out of battery. I have never had that happen before, so I took everything apart again, and found that I had to set the gas block back forward to where it was before for some reason. The bolt doesn't get hung-up in the extension without the gas tube, so this is a first for me.
Anyway, gas tube alignment is pretty critical with an AR15. If the flange on the tube is being clipped by your carrier key, it will rear its head in accuracy and reliability, once the chromed inside of the key wins the war with the stainless tube flange, and you lose your gas seal. Get it right, and your gun will run like a champ for thousands of rounds. Get it slightly wrong, and it won't shoot well, then will start short-stroking. I've seen it happen in reality, and it is easily missed.
Having even a slightly misaligned gas tube because of barrel nut tooth timing is often the cause. If you are able to get a perfect alignment by looking through the rear of the receiver, then by all means, use that successful technique. I have a very focused eye when doing it, and I look at the front of the receiver, with a nice TDC reference.Last edited by Guest; 01-02-2014, 01:41 AM.
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Originally posted by LRRPF52 View PostWhen you start to look at gas tube alignment inside the upper receiver when going through your trouble-shooting stage with a stripped Bolt Carrier, it can make a huge difference.
I disassembled my 16" Grendel just to check the squareness of the face, and reassembled it. As I was installing the gas block with tube attached, I wanted to see if I could just mount the rear of the block flush with the shoulder on the barrel profile step, so I determined my gas port locations, and found that I could.
Once I got the block positioned (it's a JP that I modified), I went to check my Bolt Carrier interface with the gas tube, ensuring that there was no binding. I clamped it down, and re-tested the BCG, which promptly got hung up from coming out of battery. I have never had that happen before, so I took everything apart again, and found that I had to set the gas block back forward to where it was before for some reason. The bolt doesn't get hung-up in the extension without the gas tube, so this is a first for me.
Anyway, gas tube alignment is pretty critical with an AR15. If the flange on the tube is being clipped by your carrier key, it will rear its head in accuracy and reliability, once the chromed inside of the key wins the war with the stainless tube flange, and you lose your gas seal. Get it right, and your gun will run like a champ for thousands of rounds. Get it slightly wrong, and it won't shoot well, then will start short-stroking. I've seen it happen in reality, and it is easily missed.
Having even a slightly misaligned gas tube because of barrel nut tooth timing is often the cause. If you are able to get a perfect alignment by looking through the rear of the receiver, then by all means, use that successful technique. I have a very focused eye when doing it, and I look at the front of the receiver, with a nice TDC reference.
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Just when you think you have figured this little guy out, something pops up and blindsides you. Back in 2002, I thought I knew the AR15 inside and out, just because I had memorized every component down to the springs and detents, and had been living with them for all of my adult life (M16's and M4's).
While I was familiar with the parts and their locations, and what they were supposed to do, I didn't know a fraction of what I have learned since then when I really dove into working on them. You could basically pick any part on the gun, and there are things you never knew about it, the peculiarities of the materials, why certain alloys were sourced over others, and how they are supposed to interact with other parts.
I never knew all those years that the Mil-spec called for the carrier key to be chrome-lined, and that the steel on the carrier key was supposed to be softer than the anodized upper receiver. I could go through every part of the gun now and explain many things I didn't know back in 2002, when I thought I was pretty knowledgeable on it after shooting them and maintaining them since the 1980's. I basically knew squat, and have just learned to realize the more I learn, the more I realize how little I know.
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Originally posted by LRRPF52 View PostJust when you think you have figured this little guy out, something pops up and blindsides you.
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I basically knew squat, and have just learned to realize the more I learn, the more I realize how little I know.If it's true that we are here to help others, then what exactly are the others here for?
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It's nice to have other people make the costly mistakes for a change When I first started working on my Colt AR-15 in 1979 I had a detente and spring fly out of my rifle on to my bedroom multi color rug. My first thought was, "what the hell was that"? Parts were only available from colt and took months to acquire. Needless to say it took me all night to find them . I was working off a picture schematic I copied off a book from the public library. Needless to say we have come far with information and friendly help like on this forum.
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I don't look at anything when lining up the gas tube hole to the barrel nut and upper receiver. I tighted the barrel nut to the snug position, 20ft lbs or so, the next hole will be as tight as it will need to be. I put the gas tube thru the upper toward the barrel nut (Backwards direction) and apply a little pressure, or have my son push it softly toward the barrel nut. When it lines up, it slides thru. Then I pull it out and it goes right in from the other side.
So my son is not always there. So I put a rubber band on the end of the gas tube, I use an old rubber barrel thread protector as a cup, put the other end on a quick disconnect picatinny block, I mounted to the upper rail, and again, apply a little pressure using the rubber band and wala, it pops thru when the hole lines up as I tightened the barrel nut and the gas tube holes are lined up.
I've done numerous uppers this way and all work fine, gas tube to carrier key, you always have to go to the next hole so don't under tighten. If it feels to tight and you haven't gotten to the hole for line up, loosen the barrel nut back a 1/4 turn and it will turn a little further the second or third time you tighten it. You don't have a lot of chances so apply the correct pressure and then use the gas tube as your feeler gauge. Well thats what I do with success.
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Originally posted by LRRPF52 View PostI basically knew squat, and have just learned to realize the more I learn, the more I realize how little I know.
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Then factor in how many trips we actually have ridden around the sun, and you are forced with the reality that we are basically living by the Grace of somebody with a heck of lot more experience than we could ever accumulate in the totality of our combined lifetimes.
This current generation is riding on much of the engineering work done in my dad's era, and most haven't the slightest clue why the wonderworld of technological fantasy land exists at their fingertips and ADD demand cycle. That's why it gives me hope when I see young guys who pursue STEM degrees, some of whom are members here on the forum.
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[QUOTE][LRRPF52...Anyway, gas tube alignment is pretty critical with an AR15. If the flange on the tube is being clipped by your carrier key, it will rear its head in accuracy and reliability, once the chromed inside of the key wins the war with the stainless tube flange, and you lose your gas seal. Get it right, and your gun will run like a champ for thousands of rounds. Get it slightly wrong, and it won't shoot well, then will start short-stroking. I've seen it happen in reality, and it is easily
missed./QUOTE]
Years ago I had an AR That started to short stroke after a couple thousand rounds. I got all the same answers from people about what to check, but it took me taking apart the thing and measuring the flange on the gas tube to figure it out. The gas block was installed very slightly off center. Replaced the gas tube, Since then I have many times that through it without a single problem.... Where was this info 10 years ago?quis posuit in mea ocreis bologna!
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Originally posted by dega37 View PostWhat do you all use for the barrel vise between the clamps and the barrel?
I use Delrin or Urethane. You can get them at hardware stores.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
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