What would be the best way to replace a gas tube on a upper with a pinned muzzle device? My upper is a 14.5" carbine length with a FSB and a 7" rail. Is it as simple as punching out the FSB, sliding it forward and sliding the gas tube under the rail into the receiver or would it require additional steps?
Yes that would work. Or you could punch out the gas block roll pin and pull the tube out the receiver end. It’s not necessary to pull the FSB in most cases.
There’s a step down bend in the gas tube on 99% of the gas tubes out there, not sure how you’ll get that through the receiver. The only uppers I’m aware of with competely straight gas tubes are the Colt 6940 an the LMT MRP. With the MRP you would just pull the entire barrel the change the gas tube.
It depends on the type of rail really. If you had say a two piece DD Omega or a two piece Troy rail you could remove the rail without having to move the FSB to get the gas tube changed.
If you have a solid rail then moving the FSB forward so that you can change the gas tube would be necessary.
I was able to remove a gas tube without removing the fsb by just punching out the roll pin and finaggling it out. It is a little flexible. Getting it back in was a little more difficult than removing it but not too bad.
My rail is a 1-piece DD M4. How would one align the gas tube and the carrier key without removing the rail?
Pretty much impossible w/o removing the rail and FSB.
It should be ligned up with the fsb on the barrel I would think. If your fsb is straight up and down, the gas tube should be lined up with the carrier key. You’ll have to knock out the taper pins in the fsb though. It’s pretty easy. They punch out from the left side.
Sounds about right to me.
Often times when I am doing maintenance / inspections I will take the gas tube out, or replace it via the receiver without punching out the FSB. A little wiggling will do it. Some heavy carbon or gunk build up around the gas tube hole in the receiver will require more wiggling but no biggie. You can also punch out the gas tube wiggle it towards the receiver. When it comes out of the FSB you can rotate the gas tube and pull it out of the receiver towards the muzzle end past the FSB.
For your task, I don’t see any reason why you can’t just knock out the FSB pins pull the FSB forward towards the muzzle, clearing the upper receiver, punch out the gas tube roll pin, pull out the gas tube from the FSB towards the upper receiver, then just pull the gas tube out the muzzle end.
Install would be in reverse. The stock barrel nut with its notches is what generally makes the gas tube out of alignment with the gas key and that is what needs adjusting. With the DD barrel nuts, unlike the stock nut, D ring and spring, installation of the gas tube in reverse should be straighforward.
If you didn’t want to punch out the FSB pins, you could punch out the gas tube roll pin, use a pair of needle nose pliers, reach in via the ejection port wiggle the tube out the upper receiver. Be aware of 2 things. DO NOT ding up the bell on the gas tube with the pliers and with a high round count weapon, the gas tube may be difficult to separate from the FSB. Break free and heat may be necessary.