Flash hole liner

[Pioneer flinter]

Hey fellas i just made a new flash hole liner from a carbon steel grade 8 bolt. I noticed all of the factory produced liners are stainless. Should i have any concerns about using the carbon steel bolt? Thank you all.

 

[Black Hand]

Chambers sells a steel liner (not stainless).

 

[Artificer]

After looking at the following linked chart, it appears you chose a good bolt to make the liner from.
https://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx

However, I would very much like to see Zonie's take on this.

Gus

 

[Elnathan]

Eeeh.

Do you happen to know what the carbon steel is and what hardness it has been tempered to? I'd be worried that it was tempered too hard for shock impact and thus be too brittle (i.e., tempered for wear bend resistance like a knife blade, at 55-60 rockwell, instead of a gun barrel at 30 rockwell).

 

[Crewdawg445]

Eeeh.

Do you happen to know what the carbon steel is and what hardness it has been tempered to? I'd be worried that it was tempered too hard for shock impact and thus be too brittle (i.e., tempered for wear bend resistance like a knife blade, at 55-60 rockwell, instead of a gun barrel at 30 rockwell).

Grade 8 will be just fine. Only difference between the two metals will be longevity. Obviously stainless will outlast the alloy. With a tensile strength of 150,000lbs per square inch you certainly wont have any issues!

 

[Vaino]

On my first build I used a 1/4-28 SS set screw and that was in 1976 and it's still in the LR which was shot a lot on squirrels. Don't know of any good reason why a steel TH liner would be used.....I now use Chambers' SS "White Lightning" TH liners in all my builds....Fred

 

[Elnathan]

Grade 8 will be just fine. Only difference between the two metals will be longevity. Obviously stainless will outlast the alloy. With a tensile strength of 150,000lbs per square inch you certainly wont have any issues!

Tensile strength is what you look for if you are going to hang a bridge off it. Toughness is what you are looking for to take the shock of an explosion. Two very different requirements, and just because a piece of metal has a high tensile strength does NOT mean that it has a high degree of toughness. Steels are cold drawn to increase tensile strength via work-hardening - they won't stretch under higher loads - but tend to be more brittle as a consequence, for example. Likewise, there are very good reasons why a file, a knife, an axe, and a gunbarrel are heat treated differently.

A grade 8 bolt may be fine, and I suspect that such bolts are tempered more for toughness than wear resistance. I'd want to know, though, be before shooting it, or standing on the vent-side while someone else shoots it. I figured that the OP might be interested...

 

[Crewdawg445]

Tensile strength is what you look for if you are going to hang a bridge off it. Toughness is what you are looking for to take the shock of an explosion. Two very different requirements, and just because a piece of metal has a high tensile strength does NOT mean that it has a high degree of toughness. Steels are cold drawn to increase tensile strength via work-hardening - they won't stretch under higher loads - but tend to be more brittle as a consequence, for example. Likewise, there are very good reasons why a file, a knife, an axe, and a gunbarrel are heat treated differently.

A grade 8 bolt may be fine, and I suspect that such bolts are tempered more for toughness than wear resistance. I'd want to know, though, be before shooting it, or standing on the vent-side while someone else shoots it. I figured that the OP might be interested...

Yes thank you for the education, as a aircraft machinist with eleven years experience in the field I'm very aware of the above information and metallurgy. The grade 8 liner will outlast the barrel, period. No need to "overanalyze".

 

[rich pierce]

It will be great for this purpose and look good too. A shiny touchhole liner is offensive to me on a barrel with blued, browned, or a patinated finish.

 

[Elnathan]

Yes thank you for the education, as a aircraft machinist with eleven years experience in the field I'm very aware of the above information and metallurgy. The grade 8 liner will outlast the barrel, period. No need to "overanalyze".

Well, I'm neither a machinist nor a metallurgist, but I do know enough to be worried when folks start citing tensile strength for applications requiring toughness.

If you know what grade 8 bolts are actually made of and how they are tempered I'd be interested to hear it. Potentially very useful information.

 

[Crewdawg445]

Well, I'm neither a machinist nor a metallurgist, but I do know enough to be worried when folks start citing tensile strength for applications requiring toughness.

If you know what grade 8 bolts are actually made of and how they are tempered I'd be interested to hear it. Potentially very useful information.

Most grade 8's are medium carbon alloy steels, not full carbon steels but ultimately a mix, which in turn gives them a high psi strength. Also the pre load strength is much higher which yields greater strength in the threads.

They also are usually quenched at 800 degrees and normally heat treated on a rockwell scale of 34-39 C.

For a liner, absolutely fine.

Forget to mention we use allot of grade 8 hardware on aircract, very important and considered a critical application you absolutely DO NOT want to mix grades example: grade 8 bolt and grade 5 washer. We also safely wire everything but correct hardware is critical to the overall comprehensive strength of the fastener for a reason. Mainly these type of bolts are used on engine components and pylons just to name a few.

 

[Artificer]

It will be great for this purpose and look good too. A shiny touchhole liner is offensive to me on a barrel with blued, browned, or a patinated finish.

Very much agree! I know our modern barrels are not made of Iron and are made very differently than original barrels; but I also like being able to brown/blue/patinate a liner so it doesn't stick out like a sore thumb like a SS liner does. It isn't a matter of function, rather a matter of personal taste.

BTW, Spence has posted a few pics of original Iron barrels that were repaired using Iron "Vent liners/plugs" when the flash holes burned out and they also blended in quite nicely.

Gus

 

[Crewdawg445]

Very much agree! I know our modern barrels are not made of Iron and are made very differently than original barrels; but I also like being able to brown/blue/patinate a liner so it doesn't stick out like a sore thumb

Gus

Agreed in all ways Gus! I myself unfortunately must admit of being guilty in using stainless white lighting liners... My OCD tendencies get in the way sometimes and its nice knowing that liner by golly won't be going bad... hehe.

 

[Artificer]

Thank you for providing the info on the Grade 8 bolt and especially the Rockwell Hardness range.

FWIW, back in the late 80's a good friend needed a replacement nipple for his Navy Sharps and Hankins Rifle and of course none were available. I was fortunate we had a Rockwell Hardness testing machine in the shop and must admit I was a bit surprised the original nipple ran Rockwell C 42.

I used the hardenable tool steel we had in the shop along with our heat treating oven and got the replacement to the same hardness on the third try, after properly annealing it.

I mention this as another example the Grade 8 bolt will be just fine for use as a liner.

Thank you.

Gus

 

[Crewdawg445]

You are welcome Gus! Enjoyed reading your experience.

 

[Elnathan]

Most grade 8's are medium carbon alloy steels, not full carbon steels but ultimately a mix, which in turn gives them a high psi strength. Also the pre load strength is much higher which yields greater strength in the threads.

They also are usually quenched at 800 degrees and normally heat treated on a rockwell scale of 34-39 C.

Thanks.

For comparison, military standards for 4150 series barrel steel are 28.8-35.5 Rockwell. I think most commercial 4140 barrels are in the 29-32 range. Sounds like they are roughly comparable, given differences in alloy.

 

[Crewdawg445]

Never checked the hardness of our M4 barrels, be interested to find that out on the vulcan cannon of the F-16 which is CR- MO-V steel... Worked the jets for years. Next time I have the terrible opportunity for arms inventory I'll likely see. Makes sense, machine gun steel is a 41V45 steel which is essentially a proprietary blend that is hammer forged CMV. Very tuff and good steel that gets work hardened due to the forging process. Absolutely nothing but over kill on semi-auto weapons and certainly that for a muzzleloader barrel or touch hole liner.

 

[Zonie]

...

However, I would very much like to see Zonie's take on this.

Gus

The grade 8 bolt will work fine for a touch hole liner.
It will wear out from hot gas erosion faster than stainless steel would because it doesn't have the chrome and nickle in it that gives stainless its corrosion and hot gas erosion resistance.

As for strength, a grade 8 bolt is overkill. A plain steel carbon screw would work for a liner just as well.
Nothing wrong with overkill though. After all, the barrel on your muzzleloader is made out of a low carbon steel so the threads in the barrel will fail from load (read tensile strength) long before your liner will and the threads in the barrel are sufficiently strong to do the job they have to do.

As others have mentioned, using a carbon steel for a vent does give you the option of browning or bluing the liner. To some, the better look is worth it. Others are happier using the long lasting stainless steel.

 

[Pioneer flinter]

Thank you all for your input and all your knowledge. I like the way it browned up. I fired some lite blank loads through it in my back yard lock time was very good. once again thank you all.

 

[DBoon]

I've been using 1/4 X 28, grade 8 for many years on my guns and with no problems or complaints. SS is not something I like to look at since it is not traditional. SS is tough and will no doubt give endless service, but if tradition is a factor then the grade 8 is an excellent alternative IMHO. My buddy, Jack Hubbard, also favors grade 8.