AR Sponsor
Posted: 7/3/2013 8:06:32 PM EDT
|
I am building a new upper. The gas tube hangs up on the lower portion of the port going into the upper receiver. Any advice?
|
|
Quoted:
The barrel nut is lined up correctly. I've built several over the years but never run into this problem. I think the port cut into the upper receiver is too high. They have threaded bushing in there. I think I'll need to open it wider There should not be any bushing unless the upper is designed for a piston system |
|
The proper way to check for this is to remove the bolt from the BCG and cycle it into the upper upsidedown. It's not uncommon to have to bend the gas tube with a large screw driver to tune it to the gas key.
For whatever reason, I've had a few of these happen to me lately too. 
|
|
Ok, so bending the gas tube doesn't work.
I have a YHM FF handguard. As the gas tube goes through the barrel nut, it holds it lower on the bushing. This is where it is hanging up. So it comes back to either getting rid of the bushing and let it be very loose in the port, or grinding down the lower portion of the bushing. I don't think that I want to grind on the barrel nut. |
|
Strange there's a bushing in there. Like an Adams Arms piston conversion kit bushing?
Like this? |
|
My take is that grinding out the hole is a bad idea.
The hole is not an interference fit to the gas tube but it does restrict the movement of the tube enough that it will stay in alignment with the gas key during firing. If the hole is in the wrong position send the upper back. I have never had a misdrilled YHM barrel nut, but it is possible. So if the gas key also does not line up then you know the upper is out for a DI application.. An armorer’s alignment gage, a drill bit, a steel rod, etc. put in the gas key should go through the hole easily when the bolt carrier is put in the upper. Obviously a person can cause damage with a drill bit if not careful. I don’t use piston kits, but it seems like there is a kit where the hole is drilled and a bushing installed. |
|
Quoted:
What is weird about this is a bushing doesn't change the location, just reduce the size and reinforce the hole with steel. Yes, but he makes it sound like it nearly works, just hitting the bottom of the bushing (which AFAIK, should not be there). Pics would be great, as well as more info in the acquisition of the upper (was it used, new second hand, could someone have been prepping it for some custom application like a piston build? Can it be returned?). Has ANYONE here ever seen a standard upper with a bushing in the gas tube opening? |
|
Quoted:
Quoted:
What is weird about this is a bushing doesn't change the location, just reduce the size and reinforce the hole with steel. Yes, but he makes it sound like it nearly works, just hitting the bottom of the bushing (which AFAIK, should not be there). Pics would be great, as well as more info in the acquisition of the upper (was it used, new second hand, could someone have been prepping it for some custom application like a piston build? Can it be returned?). Has ANYONE here ever seen a standard upper with a bushing in the gas tube opening? I would try to get the bushing out. As everyone has stated, it doesn't belong. Better yet, I would contact the seller and ask WTF? and arrange for an exchange. |
AR Sponsor