Is this a helicoil?

[longcruise]

Cleaning a GM drop in barrel today and saw this. It looks like a stainless steel helicoil in the nipple threads. The crossways piece in the bottom seems to be from the helicoil having turned itself in beyond the threads that hold it. I've had this barrel for a long time now and today was the first time this appeared. It's not something I previously overlooked. It's too obvious when you go to reinstall the nipple.

I have heard of helicoil problems in the past with GM barrels but I thought they were used on the breech plug threads.

What do you all think?

 

[hawkeye2]

Looks like one to me.

 

[sawyer04]

Yep, looks like a helicoil to me too.

 

[Jaegermeister]

I say yes.

 

[Zonie]

As far as I know, no one has ever used a Helicoil for a breech plug thread repair but yes, that is a Helicoil in the nipple hole. It's a pretty common fix. As I recall, both Green Mountain and Thompson Center have used this repair when the threads the factory machined into the barrel didn't meet spec.

The thing you see at the bottom of the Helicoil is the tang that is used along with a special driver to screw the Helicoil in. It is supposed to be broken off and removed after the insert is in place.

You might want to make sure the Helicoil isn't blocking off the flame channel that goes from the bottom of the nipple hole to the breech.
Helicoils are sometimes too long for the installation and if they are, the reliability of getting the gun to fire can be reduced.

 

[longcruise]

In this case it looks like the helicoil has been turned deeper into the threads until it was pushed beyond the threads in the bottom. Likewise, there are threads exposed at the top that the helicoil has been turned in deeper than.

My explanation of this is lacking.

I'm going to call GM on Monday and see what they say about it.

I bought it new and never did any mods to it so it must be factory. The better fix would be to drill and tap for an oversize nipple but in Terms of meeting specs in order to sell it they probably have to make a .250x28 fit.

I'll follow up on the forum.

 

[Carbon 6]

The story goes something like this.
GM installed metric nipple holes. As a fix GM, drilled out the metric holes, put 1/4-28 Heli-Coils in, and installed the proper nipple. That did not fly because was folks did not want new barrels with Heli-Coils. As a result GM replaced a bunch of breech plugs.


From GM.


Notice to Owners of our Black Powder "Drop-In" Barrels: There is a possibility that the nipple on your rifle is defective. Metric threaded nipples were inadvertently installed in some barrels instead of the proper 1/4-28 threaded nipples. The serial number range in question if for percussion barrels # 030672 - 031352. Do not fire this rifle. Please contact us at 603-447-1095 x18 or [email protected] to arrange return shipping. The barrels will be inspected and if found compliant returned. If they are discrepant the breach plugs will need to be replaced so bear with us as this may take a while to complete. We apologize for the inconvenience.

 

[longcruise]

hmmmm. Mine doesn't fall in that sn range.

Wondering what to expect from GM?

 

[hawkeye2]

It's possible a previous owner damaged the threads and repaired it before you got it.

"In this case it looks like the helicoil has been turned deeper into the threads until it was pushed beyond the threads in the bottom. Likewise, there are threads exposed at the top that the helicoil has been turned in deeper than."

I believe you are correct or it's possible that the installer pulled that thread out of place when they broke the tang off. The tang would have been directly across the hole and not like that piece. I would probably remove and replace that one but if it doesn't bother you or hasn't given any trouble.....

 

[longcruise]

I was the original owner so it must have been the factory that did it.

It it's not satisfactory to me to have a helicoil repair. If GM won't fix it I'll drill and tap for oversize or replace the breech plug.

 

[Carbon 6]

hmmmm. Mine doesn't fall in that sn range.

Wondering what to expect from GM?

I think GM had two separate recalls and I only posted the one.
I would still call them.

 

[Zonie]

I was the original owner so it must have been the factory that did it.

It it's not satisfactory to me to have a helicoil repair. If GM won't fix it I'll drill and tap for oversize or replace the breech plug.

I would just remove the broken thread at the bottom and use the barrel like it is.

The thread on the nipple should be a 1/4-28. That is a standard thread size for nipples.
The Helicoil tap that was used to prepare the hole for the 1/4-28 UNF insert is a .300-28. That is, the major diameter of the thread is .2995 and the thread pitch is .03571.
Since the major diameter of the threaded hole is only .015 smaller than a 5/16 thread, there isn't enough material to thread the existing hole for a 5/16-24 threaded nipple. That is the next larger size standard nipple thread and it is used on percussion muskets.

Here is a drawing I made of a 1/4-28 Helicoil with a standard nipple screwed into it. I made it back when this issue of using a Helicoil to repair nipple threads and people were saying Helicoils are used all the time to repair spark plug holes.

Although there is very little sealing surface for a nipple, there are a lot of places where the nipple screws directly into a round drum and in that case, there isn't a real sealing surface either.
A Helicoil isn't a real good repair but it is stronger than a hole without one and it is totally safe to shoot a gun that has a Helicoil installed for the nipple.

 

[longcruise]

Great information, Zonie. Thanks.

 

[SDSmlf]

Within the past week contacted Green Mountain through their website about two barrels, neither ever shot, that were within the serial number range of previous recalls. Concerned about possible Heilcoil use in nipple hole. Received an email within an hour wanting to know package size...

Go to GM website and contact them. Tell them what you have and what your concerns are. Expect they will quickly respond.

FYI. Currently have four GM barrels. Three of the so called LRHs and one roundball barrel. No complaints. Great customer support.

 

[Mad Professor]

Cleaning a GM drop in barrel today and saw this. It looks like a stainless steel helicoil in the nipple threads. The crossways piece in the bottom seems to be from the helicoil having turned itself in beyond the threads that hold it. I've had this barrel for a long time now and today was the first time this appeared. It's not something I previously overlooked. It's too obvious when you go to reinstall the nipple.

I have heard of helicoil problems in the past with GM barrels but I thought they were used on the breech plug threads.

What do you all think?
View attachment 14840
View attachment 14841

I had one like that from GM ~ fall 2005. Threads hung down too low and installation helicoil tang in the way too. I wasted a good amount of lead and powder trying to figure out why my new barrel was giving misfires. GM would have replaced the breech plug but I needed the rifle for deer season. I snapped off the bottom few coils that were in the way and no more miss fires. I still contemplate sending it back for a new breech plug, but it's dialed in to shoot now so I've lived with it.

 

[longcruise]

Got in touch by phone yesterday. They requested an email with full info which I did late yesterday and included the same pictures from this post. Should hear something soon. They were very helpful.

 

[SDSmlf]

As I mentioned in post #14, GM is very quick getting back to you on inquiries. They responsed to my initial email in less than an hour, and I had the UPS prepaid label to return the barrels by the following morning. And this is for barrels made over 10 years ago.

 

[longcruise]

Update. Called them Tuesday afternoon and before the day was out had a return label in my email.

 

[SDSmlf]

Update. Called them Tuesday afternoon and before the day was out had a return label in my email.

Package with both barrels I previously mentioned was delivered today. Based on previous dealings with Green Mountain expect both barrels are checked, repaired if required, and returned by end of next week.

 

[nkbj]

I've had mixed results with Green Mountain.
Had great customer service for drop-in barrel parts.
But then again, I've had a barrel come in that's .5% off on groove diameter and their response was a brush off, that it's within specs.

They made the mistake of not remembering the basic premise for repeat sales...
"They may not remember what you said but they will remember how you made them feel."
Good bye, Green Mountain.