Safe Practice to Consider

Quote:

---

Originally Posted by terrym

Very informative post, you seem to have expertise here. Getting back to the rust thing though, this example shown as evidence is a stainless steel barrel. What do you think are the odds of rust in a screw hole being sufficient to cause such a failure?

---

This is why I don't think that there is much of an issue with the screw hole, yes it is weaker, yes there is a chance but the chamber area of the gun is never tapped, it is always ahead of this where the pressure is lower. Since the bullet is already moving by this point the pressure is not at its peak as it would be the instant before the bullet begins its trip down the barrel. This is why you see pressure graphs with spikes, the highest peak is at the point where the gasses have built up their maximum pressure before the bullet moves.

Stainless steel though can corrode, it does it all the time it just does not go as soft as iron oxide (rust) or as quickly. You can get pitting in stainless, you can get creep corrosion in stainless and you can get galvanic corrosion in stainless, the galvanic is the fastest and the worst. Galvanic corrosion is cool though, if you have 2 materials with very different internal charges one will corrode thereby keeping the other safe. Since this has to be in an electrolyte they use this technique for ships hulls and pipeline systems. Blocks of zinc are bolted to the ships hull, the zinc will corrode and protect the steel. They tried this in cars but air does not have enough electrolyte in it to protect the car and cars have tons of isolators in it so keep this idea from working too well.

Back to the original post, if you have the hole open you can get trapped water in there and start to rust the steel, this rust can work its way in and pit heavily which could cause a problem but I still highly doubt that would happen in a real world situation. Proof testing of barrels is required on all modern firearms, hence the "Proof Marks" on all firearms, in the early days you can link the age of a firearm to the stamp they used at the proof houses.
These proofs are significantly higher than the standard operating pressure of the firearm, this is why I cannot believe that a tapped hole (done properly and not too hot) could cause any failure irrelevant to if it were filled or not. That being said if you wanted to tap a thin walled barrel like a shotgun the gunsmith may advise against it due to the risk of going through the barrel. I have a 410 that I had sights put on for use with slugs and the gunsmith tapped the hole at the muzzle and dovetailed the rear because his machining practices lead to a greater control of depth on the dovetail and no risk of causing the metal in the barrel to press down into the barrel.

Quote:

---

Originally Posted by ET1

Having seen numerous pictures of barrel ruptures especially some with the 10ML-II one split of the barrel always seem to run through the rear screw hole. Coincidence, I don’t think so.


Attachment 28123


Ed

---

Still claim to not be insinuating that screw holes don't cause barrel failure? The entire premise of this thread is exactly this topic. For someone who likes to imply they are of a higher level on everything related to firearms, a guy who feels discussing the optimal pressure curves of expanding gasses on a forum like this, some here have questioned your advice and or motives. You are the one who drops the Engineer title and every third sentence it seems like. Anyway you are too predictable and obvious here. I'll leave you to your audience. But I can't help but repeat:
Where is the manufacturer of rifles and barrel data supporting your claim of these screw hole failures? Unless this is in your next response please don't bother, I know I'm done with this/you.

Quote:

---

Originally Posted by terrym

. I'll leave you to your audience.

---

Thanks that all we ask....LOL...

Quote:

---

Originally Posted by Fox

This is why I don't think that there is much of an issue with the screw hole, yes it is weaker, yes there is a chance but the chamber area of the gun is never tapped, it is always ahead of this where the pressure is lower. Since the bullet is already moving by this point the pressure is not at its peak as it would be the instant before the bullet begins its trip down the barrel. This is why you see pressure graphs with spikes, the highest peak is at the point where the gasses have built up their maximum pressure before the bullet moves.

---

Fox

I have a problem with your theory of pressure relationship to bullet moving.
Quickload program also says different as the bullet is moving before peak pressure is achieved.

Attachment 28129



Ed

Quote:

---

Originally Posted by ET1

Fox

I have a problem with your theory of pressure relationship to bullet moving.
Quickload program also says different as the bullet is moving before peak pressure is achieved.

Attachment 28129



Ed

---

I had read once that this was related to the pressure from the primer explosion, especially with the original shotgun 209 primers causing the bullet to move prior to full ignition. Now this was in relationship to BP as opposed to smokeless, so that may negate the comment.

No. Plugging the hole with a set screw will not add back reinforcement.
A round hole is not a sharp feature that will cause a sharp stress riser. This is why in RT, MT, PT, UT and even VT evaluation criteria rounded indications of certain size (dependent on which code) are allowable. Also why in structural members any (whether for lightening or for pass though of any other piece) holes must be round or have rounded corners.

A crack in a cylindrical pressure vessel (and that's really what a barrel is) will always propagate longitudinally as, practically speaking, "hoop stress" will always be higher than axial stress. Hoop stress is caused by the pressure acting radially from the center of the cylinder on the walls of the pipe/vessel in the circular x-section. Axial stress is caused by the pressure acting on the ends of the vessel (in the barrel this would be the breech plug and the projectile or barrel obstruction). I cannot explain why in barrels they seam to peel in 2, 3 or 4 places. In pressure vessel it is normally in 1 tear in the least reinforced, or most highly loaded axis (in a horizontal vessel the bottom of the vessel is slightly more highly loaded as it is under the the pressure but also under the head/weight of the whatever the vessel contains).

You can test this yourself. Fill a copper pipe (or even a cylindrical pop bottle) with water and cap both ends, throw it outside for a bit. Tell me which way it splits.

Certainly the hole, blind or not, within the barrel reduces the strength of the barrel. Plugging it with epoxy or a set screw isn't going to add integrity back into it, they are not molecularly bonded/fused. Plug welding would but then you are going to potentially warp the barrel, and damage the metallurgy in the area you are welding.

I would be more concerned if you are putting a screw in the threaded hole that it be stainless so as not to introduce any carbon contamination which can and will cause rust within the hole/threads that can propagate. Also putting a metal of different grade in that hole could cause additional stress as the barrel and plug would have different thermal expansion factors - albeit probably not enough for any serious or catastrophic effects.

MikePal

IMO I don’t think there would be much difference of bullet movement before peak pressure between smokeless and BP other than distance traveled by bullet. As seen by the video you graciously provided showing demonstration of different powder burn rates.
The 209 primer can also move bullet loads in the 10ML-II if powder doesn’t immediately ignite usually causing a misfire. Another reason I suspect this holds true is that the load in ml’s has no lands to overcome (restricting movement) as found in CF rifles.
So the theory goes anyway. :)



Ed

I would have to make a few assumptions on my part but I would believe that the pressure can be higher after the projectile begins to move. The projectile will move once the friction holding it in place has been overcome. The pressure causing this force may well be below the maximum pressure a given load of powder creates, and pressure may build faster than the volume (of the space behind the bullet) grows until the bullet gets some distance down the barrel, the bullet is moving ever faster and the powder charge is used up.

Just my opinion. I am not an Engineer, but I've dealt with some...and I think they stayed at a Holiday Inn.

Fishy Wishy

Tell you what read B31.3 of the ASME Code under Severe Cyclic Pressure Piping and tell me what it visually allows for surface porosity. I know that the procedure I'm required to use for dye checking has zero tolerance for even the smallest porosity for B31.3 Severe Cycling. Wonder why.

Any threaded area is considered having sharp stress risers and where accessible are usually checked with Dye or Mag inspection if NDT is required especially in-service components. You can argue that point with CSNDT who trains inspectors for CGSB certifications.
I know as I hold Level-2 RT-MPI-LPI along with Level-1 UT CGSB certifications.


Ed

Quote:

---

Originally Posted by Fishy Wishy

I would have to make a few assumptions on my part but I would believe that the pressure can be higher after the projectile begins to move. The projectile will move once the friction holding it in place has been overcome. The pressure causing this force may well be below the maximum pressure a given load of powder creates, and pressure may build faster than the volume (of the space behind the bullet) grows until the bullet gets some distance down the barrel, the bullet is moving ever faster and the powder charge is used up.

Just my opinion. I am not an Engineer, but I've dealt with some...and I think they stayed at a Holiday Inn.

---

Quickload agrees with your assumption.
And as seen the bullet is continuously accelerating while in the bore.

Ed