Welding oversized gas port?

[sidewaysil80]

I have a brand new 6920 barrel that I sent off to have cut down and the port opened up to .070”. Unfortunately the gas port was overly enlarged due to an internal communication issue at the shop. I want to reuse the front sight post/gas block so simply installing an adjustable gas block is out of the question.

The shop is incredibly helpful and offered to either weld the port and redrill or replace with a new Colt barrel (in another email). I don’t want them to have to source a new barrel if the weld method is equally or even stronger than a factory gas port. But I’m unsure how durable it would be and if would erode quicker or be a weak point. Has anyone ever heard of this technique or is familiar with welds on a gas port? Here is there explanation below...


For "repair", the hole can be laser welded and re-cut. The weld does NOT get into bore line so no worries of burrs. If for any reason we look at it and decide that isn't a suitable fix, we'll replace the barrel with a new one. We've closed holes with the welding/re-cut in the past for various reasons and it has always worked fine. The welding is via a microscopic laser and it leaves very little weld on the barrel surface. But that all gets cleaned up. Barrel shouldn't need re-parking but if it does we use the same parkerizing solution Colt and other .gov MFGs use.

[Inkslinger]

Try this. This is product developed by member Clint.
http://www.blackrivertactical.com/concrete5/customtune-gas-port/

[sidewaysil80]

Try this. This is product developed by member Clint.
http://www.blackrivertactical.com/concrete5/customtune-gas-port/

Thanks, I’ll look into that more when I get home. I wonder how it would compare to welding and redrilling in terms of longevity and erosion.

[Inkslinger]

Thanks, I’ll look into that more when I get home. I wonder how it would compare to welding and redrilling in terms of longevity and erosion.

Erosion of the port is more of an issue in the bore, so I don’t think it would be an issue.
https://www.m4carbine.net/showthread.php?170289-Gas-Port-Erosion-of-AR-15-Barrels
https://uploads.tapatalk-cdn.com/20180427/c809a36f81ef904fb951e283b7c76aa2.jpg

[HeruMew]

I dunno...

You're talking nitrocarburized steel. Any metal they add to it will wear faster. Significantly faster. I just can't imagine how they would get it really precise and pentrated weld without risking metal getting into the barrel itself or only lightly tiging it and, again, risk of lack of penetration and wear resistance.

I am no shop worker or metallurgist. So, Your Mileage Will Certainly Vary.

I'd be flustered and ask them to source a new one. Just my opine though.

[Clint]

I would never recommend welding a barrel.

We're talking about a stress relieved alloy steel pressure vessel, not a mild steel trailer hitch.

If the shop is willing to replace the barrel, that is the best option.

Otherwise, a port can easily be installed into the existing FSB.

[HelloLarry]

I would not sweat it too much. Tap it, insert a set screw, drill that and grind off any protrusion. The set screw should not go all the way through.

All the erosion is going to happen in the barrel at the port, just like it was going to happen there in the first place.

Barrels are a consumable. Shoot it until it croaks.

[scottryan]

I have a brand new 6920 barrel that I sent off to have cut down and the port opened up to .070”. Unfortunately the gas port was overly enlarged due to an internal communication issue at the shop. I want to reuse the front sight post/gas block so simply installing an adjustable gas block is out of the question.

The shop is incredibly helpful and offered to either weld the port and redrill or replace with a new Colt barrel (in another email). I don’t want them to have to source a new barrel if the weld method is equally or even stronger than a factory gas port. But I’m unsure how durable it would be and if would erode quicker or be a weak point. Has anyone ever heard of this technique or is familiar with welds on a gas port? Here is there explanation below...




What barrel length did you have it cut to?

[sidewaysil80]

I’m really liking the idea of the gas block insert. It seems like a bomb proof product and simple to install. Even though they are willing to replace the barrel, they have always done right by me in the past and I think that may be a little overkill for something that is just .004” too large.



What barrel length did you have it cut to?
10.3” for m193 and 70/30 suppressor use.

[markm]

I would never recommend welding a barrel.

We're talking about a stress relieved alloy steel pressure vessel, not a mild steel trailer hitch.


This.

[MQ105]

I’m really liking the idea of the gas block insert. It seems like a bomb proof product and simple to install. Even though they are willing to replace the barrel, they have always done right by me in the past and I think that may be a little overkill for something that is just .004” too large.



10.3” for m193 and 70/30 suppressor use.

Have you test fired as-is? If not, that would be step 1 for me. If you confirm the port is too large, make/buy a GB insert.

[sidewaysil80]

Have you test fired as-is? If not, that would be step 1 for me. If you confirm the port is too large, make/buy a GB insert.

I don't need to test fire, I measured with pin gauges. I wanted a .070" port and I received a .073+" port, might seem arbitrary but I was assured they would get the exact size I requested. I want to mimic the MK18 port size since from a reliability and longevity standpoint since that was the most tested/proven of all port sizes on a 10.3" barrel.

I'm just going to order the BRT Insert. They did a wonderful job on the cut and crown and I don't want to bust chops over something that is easily remedied with the insert, especially considering they heavily discounted the service due to the delay in time and port mess up.

[MQ105]

I don't need to test fire, I measured with pin gauges. I wanted a .070" port and I received a .073+" port, might seem arbitrary but I was assured they would get the exact size I requested. I want to mimic the MK18 port size since from a reliability and longevity standpoint since that was the most tested/proven of all port sizes on a 10.3" barrel.

I'm just going to order the BRT Insert. They did a wonderful job on the cut and crown and I don't want to bust chops over something that is easily remedied with the insert, especially considering they heavily discounted the service due to the delay in time and port mess up.

Your port may be too big (likely), but each barrel is unique. Yours may run well with .073, or it may need a port smaller than .070. Also, the insert size doesn't exactly mimic the same barrel port size. I advise you to start with an insert with a smaller port than .070. You can enlarge if needed.
Of course, you can do whatever you'd like. As someone who has done many barrel port inserts over the years, I have seen a decent variation in port size among barrels with the same length, gas system, and journal size.
Let us know how yours turns out.

[sidewaysil80]

Your port may be too big (likely), but each barrel is unique. Yours may run well with .073, or it may need a port smaller than .070. Also, the insert size doesn't exactly mimic the same barrel port size. I advise you to start with an insert with a smaller port than .070. You can enlarge if needed.
Of course, you can do whatever you'd like. As someone who has done many barrel port inserts over the years, I have seen a decent variation in port size among barrels with the same length, gas system, and journal size.
Let us know how yours turns out.

No I appreciate the insight, can you explain what you meant regarding the insert not mimicking the barrel port size? Before I read your response I ordered a .070" insert kit but I don't mind adding a smaller one to test first.

[MQ105]

Because the port is farther "downstream" in the gas flow, the size acts slightly different than a barrel port without an insert. They are close, though. Your set up may need .065 (or something) for proper function. It's easy to enlarge the port insert; you can't make it smaller...

[Bob Sacamano]

Get a BRT port. Would try the .067". Funny reading the comments, I thought I was the only one that got a gas port opened up against my desires following a cut down. Wonder if we all used the same shop.

.073 is not to the point where I would be super concerned about reduced barrel life. Next go around, I cant think of a reason to get anythong other than an AndroCorp 10.3" with .070" gas port.

http://androcorpind.com/556-nato-10-3-port-size-0-070/

[Clint]

The ports do seem to flow about 5% more than a barrel port, which normally isn't enough to worry about.

Using only Mil pressure ammo, the smaller .067" is worth a try.

[mig1nc]

I installed a .067 brt insert on a 10.5" Faxon barrel.

Worked great.

So easy even a caveman can do it... Or at least an idiot like me.

Edited for clarity.

Sent from my Pixel 2 using Tapatalk

[Iraqgunz]

.073 isn't the end of the world. Of course, we have people that still think the earth is flat, so there is that.

[Tigwelder1971]

If plugging the port, drilling and tapping for a set screw and then TiG welding would be the route that I'd go.

[ScottsBad]

This is a crazy thread. The only two possible answers are: 1. A new barrel and a new gas block. -OR- 2. Get and adjustable gas block. That's it.

1. Welding a barrel is crazy and could cause weakening or warping of the surrounding material. Kinda red neck shade tree gun smithing IMHO.
2. Putting a set screw in is even crazier.
3. Using the gas port reducer might be a solution, but it might cost as much as a new barrel.
4. If you do get a new barrel, you'll probably have to get a new sight/gas block, as it is very difficult to line up drilling for a taper pin through an existing taper pin hole.

5. An adjustable gas block is probably the cheapest way to solve it legitimately.

This is why I won't buy used weapons...

[sidewaysil80]

This is a crazy thread. The only two possible answers are: 1. A new barrel and a new gas block. -OR- 2. Get and adjustable gas block. That's it.

1. Welding a barrel is crazy and could cause weakening or warping of the surrounding material. Kinda red neck shade tree gun smithing IMHO.
2. Putting a set screw in is even crazier.
3. Using the gas port reducer might be a solution, but it might cost as much as a new barrel.
4. If you do get a new barrel, you'll probably have to get a new sight/gas block, as it is very difficult to line up drilling for a taper pin through an existing taper pin hole.

5. An adjustable gas block is probably the cheapest way to solve it legitimately.

This is why I won't buy used weapons...

How do you figure the gas port reducer might cost as much as a new barrel? I just ordered it for $35...

The gas port is still smaller than 90% of the 10.3-10.5 barrels on the market, it was just three thousandths more than I wanted. They offered a couple of solutions and I wanted to see if any other options were out there. Thread served me well as I learned of Clint’s inserts and will be using one of those.


If plugging the port, drilling and tapping for a set screw and then TiG welding would be the route that I'd go.

The inserts that are being discussed are on the gas block, not barrel. You drill/tap the gas block and insert reducer in there and then gas block slides on like normal. The insert can’t move or back out and it effectively gives you whatever port size you want.

[Tigwelder1971]

How do you figure the gas port reducer might cost as much as a new barrel? I just ordered it for $35...

The gas port is still smaller than 90% of the 10.3-10.5 barrels on the market, it was just three thousandths more than I wanted. They offered a couple of solutions and I wanted to see if any other options were out there. Thread served me well as I learned of Clint’s inserts and will be using one of those.



The inserts that are being discussed are on the gas block, not barrel. You drill/tap the gas block and insert reducer in there and then gas block slides on like normal. The insert can’t move or back out and it effectively gives you whatever port size you want.

I understand the inserts for the gas block.

On a side note, gas ports in bbls are successfully TiG welded and redone commonly.

[HeruMew]

This is a crazy thread. The only two possible answers are: 1. A new barrel and a new gas block. -OR- 2. Get and adjustable gas block. That's it.

1. Welding a barrel is crazy and could cause weakening or warping of the surrounding material. Kinda red neck shade tree gun smithing IMHO.
2. Putting a set screw in is even crazier.
3. Using the gas port reducer might be a solution, but it might cost as much as a new barrel.
4. If you do get a new barrel, you'll probably have to get a new sight/gas block, as it is very difficult to line up drilling for a taper pin through an existing taper pin hole.

5. An adjustable gas block is probably the cheapest way to solve it legitimately.

This is why I won't buy used weapons...

How does 35 equal 100+ for even a cheap barrel. 250+ for higher end.

I agree with the welding aspect, to an extent, but that's the only piece that made sense.

[MistWolf]

No I appreciate the insight, can you explain what you meant regarding the insert not mimicking the barrel port size? Before I read your response I ordered a .070" insert kit but I don't mind adding a smaller one to test first.

The gas flow in the barrel is supersonic. When a supersonic gas passes through a restriction, it is slowed to just less than the speed of sound. The rules for supersonic gasses flown through a restriction are different than subsonic gasses flowing thorough a restriction, affecting flow rate.

Therefore, the gas flow through the barrel port will be affected differently than the flow through the Micro Port.