.177 BB's

[smo]

I worked for and around Government facilities for 30 + years.

The Safety factor figured in for anything that can or could, maybe cause harm too someone or something is astronomical .
H
Even the PEL limits (Permissible Exposure Level) on lead are at a very low limit .

I’m sure there’s a lot of wiggle room in the established pressures in guns, as far as what is Safe & considered a max. load.

How is pressure measured in a gun barrel?
Do they tap the barrel and install a gauge?

 

[Britsmoothy]

There is a huge difference in the requirements of a breech loader and a muzzleloader shotgun.
The breech loader cartridge in larger than the bore considerably. The components are swaged down as they leave the cartridge case in the forcing cone and just to emphasize, that happens at a stage of maximum pressure. Then more often than not there is restrictive choking. A muzzle loader has none of this factors.

Another factor is time. Very often overlooked is just how much little time barrels are subjected to pressure.
As the pressure is so very short lived there is not enough time for the barrel to lose its integrity.
A modern barrel in cartridge rifles operate at 55,000 psi. That pressure if the barrel had to hold it for seconds would fail because the force would have time to impart motion but because only a millisecond of peak pressure exists the moment of movement of the barrel wall or a cartridge case is not reached.

It is also the same time factor that allows the use of paper or plastic shot shell hulls. There is no way you could pump thousands of psi into one of those hulls and expect it to hold it for an extended amount of time and not lose its integrity. Support it well and only a few milliseconds of high pressure and as we know they do very well.
One simply can not look and the pressure figure and deduce any high figure is bad, how high is bad? That is like asking how long is a piece of string!
Pressure is simply evidence of work. It or the devices using pressure are working.

I honestly believe black powder being listed as an 'explosive' and data charts having ' maximum' sections conspire in some minds that they see the word danger!
Then there are phrases banded about like overkill or overpressure! Over pressure, just how much over pressure caused so and so's gun barrel to fail?
"I dunno" comes back.
So how do you know it was ''overpressure" that caused it to let go then?
"I don't....but" comes back.
So you don't actually know what caused the barrel to fail, you are assuming, it's your opinion with no evidence what so ever.
" Yeah but it must of been overpressure because he told me he used more powder than listed max" comes back and so it goes.
To sum it up. If gun barrels blew up regularly because of a simple change in readily available components then:
A; guns would banned.
B; certain components would be banned.

Amazing isn't it. We fill our cars with a highly flammable liquid that can become quite " explosive" under the right conditions, drive down the freeway at speed where upon the vehilcle in front and behind are instruments capable of percussion to the degree that (and there is evidence of this) to turn our vehicle into a fireball! But somehow we live with it!

 

[smo]

My thoughts were, with a muzzle opening of .653 and using BP there wasn’t an issue..

I did start with less than 2 ozs of bb's and gradually worked my way up too the 2 oz load.

If memory serves me correctly, I don’t think I ever went over 110 grains of ffg or Fg .

But with fffg 70 grns was what worked best.

80 grns of ffg worked good as well.

 

[Zonie]

...

I’m sure there’s a lot of wiggle room in the established pressures in guns, as far as what is Safe & considered a max. load.

How is pressure measured in a gun barrel?
Do they tap the barrel and install a gauge?

There are three different ways to test the breech pressure in a gun barrel.

For very low pressures, yes, they can drill and tap into the breech and install a guage. Usually the pressures are too high and the duration of the maximum pressure is for too short of a period of time for this to be of use.

There is the "lead" and Copper method where a special chamber is threaded into the powder chamber. Into this chamber a specially shaped lead or copper slug is inserted. When the gun fires the pressure in the breech deforms the slug so, when it is removed it can be measured. The amount of deformation various pressures will cause are known, so by comparing the test slug with the known values an accurate value can be determined. The lead slug's are used for lower pressures like those in a muzzleloader. The copper slug's are used in high pressure guns like the centerfire cartridge guns.
Pressures using these methods show values as LUP for lead and CUP for copper.

The other method is to place a stress/strain gage (a transducer that converts movement into electrical signals) onto the outside of the test barrel.
By knowing exactly what the test barrels dimensions and material are they can calculate the stresses in the barrel that any given pressure inside the barrel will create.
In other words, when a high pressure exists inside the barrel, the whole barrel in the breech area (and elsewhere) will become larger and stretch. By measuring how much the barrel changes even for a very short period of time, the pressures needed to cause that amount of change can be calculated.

As for how much pressure in a shotgun barrel is safe, I don't have a good answer. I will say the Lyman Handbook shows one 12 guage load that registered 6000 psi. That was for a .690 lead roundball patched with a .020 thick patch, loaded over 100 grains of Pyrodex RS. Since they showed it, I assume they think that is a "safe" load.

 

[smo]

Thanks for the explanation Zonie.

 

[32 ballard xl]

If I understood the information that I read, 8000 psi or thereabouts for a revolver was listed as the maximum load. But I also read somewhere that someone had pushed the loads to 21,000 psi for something else (cannon perhaps?). Since rifles tend to have thicker chamber walls than revolvers, the 8000 psi is most likely safe in a modern rifle, with a considerable fudge factor.

The trapdoor Springfield arsenal loads, 45-70-500, in Army ballistic tests were conducted to assure each lot was at or below 25,000 lbs.

 

[smoothshooter]

It doesn't have anything to do with the topic but to answer your question before I retired I was a principle engineering designer. Principle in this case means leading, like the principle at a high school.

I worked at a company that designs and builds jet engines and auxiliary power units (APU). The things that provide aircraft ground power and engine starting power on the ground and in flight.

My last two big projects as Principle Designer was the APU for the Boeing 757, 767, Airbus A330 and A340. They all use basically the same APU.
The other big project was the APU for the Boeing 777.

The company was originally called AiResearch, then Garrett Turbine Engine Co. and Allied Signal. It is currently called Honeywell.

Now, back to the BB's.

It doesn't have anything to do with the topic but to answer your question before I retired I was a principle engineering designer. Principle in this case means leading, like the principle at a high school.

I worked at a company that designs and builds jet engines and auxiliary power units (APU). The things that provide aircraft ground power and engine starting power on the ground and in flight.

My last two big projects as Principle Designer was the APU for the Boeing 757, 767, Airbus A330 and A340. They all use basically the same APU.
The other big project was the APU for the Boeing 777.

The company was originally called AiResearch, then Garrett Turbine Engine Co. and Allied Signal. It is currently called Honeywell.

Now, back to the BB's.

Since we're getting technical here, which is great, isn't the word " principal ", not " principle "?

 

[Grenadier1758]

Yes, it should be Principal Engineer, but why correct a moderator when we understand what was meant?

 

[Historian]

My first real concern was over high pressure in the breech not causing the barrel to blow but causing the nipples to unseat or blow out. My second concern was the damage unprotected steel shot would have on the inside of the barrel.

 

[Britsmoothy]

My first real concern was over high pressure in the breech not causing the barrel to blow but causing the nipples to unseat or blow out. My second concern was the damage unprotected steel shot would have on the inside of the barrel.

How real is that "first real concern" sir.
I mean do you have any evidence that makes it a real concern?
Thanks.

B.

 

[Historian]

Hi Britsmoothy,
Yes, I lost a right nipple on a Navy Arms 12 SXS. Blew out the R nipple and sent the hammer back so hard it broke the main spring and gouged out a piece of wood. Gun was well maintained and rust free. My standard load for lead was, 95 grains 2Fg, leather over powder wad, 1/4 inch lubed felt, 1 1/8 oz cooper plated lead shot and then 0.30 over shot card. The waterfowl load I used was 100 grains 2Fg, leather over powder wad, 1/4 inch lubed felt, steel shot wad from BPI specifically designed for 1 1/8 oz of steel shot, loaded with 1 1/8 oz of steel #2's and then the 0.30 over shot card. We were at the range patterning the load when it blew the nipple. I had shot that load in both barrels about 20 times total when it blew. It was not fun but I am glad it happened at the range.

 

[Britsmoothy]

Hi Britsmoothy,
Yes, I lost a right nipple on a Navy Arms 12 SXS. Blew out the R nipple and sent the hammer back so hard it broke the main spring and gouged out a piece of wood. Gun was well maintained and rust free. My standard load for lead was, 95 grains 2Fg, leather over powder wad, 1/4 inch lubed felt, 1 1/8 oz cooper plated lead shot and then 0.30 over shot card. The waterfowl load I used was 100 grains 2Fg, leather over powder wad, 1/4 inch lubed felt, steel shot wad from BPI specifically designed for 1 1/8 oz of steel shot, loaded with 1 1/8 oz of steel #2's and then the 0.30 over shot card. We were at the range patterning the load when it blew the nipple. I had shot that load in both barrels about 20 times total when it blew. It was not fun but I am glad it happened at the range.

So if it was fine for 19 shots what changed for #20?

 

[Zonie]

So if it was fine for 19 shots what changed for #20?

His luck.
Actually, things had been changing with each shot.

Repeatedly subjecting a material to high stresses will lead to failure of the part. It's called fatigue, in this case, "low cycle fatigue".
It's like bending something back and forth a number of times. Each time, it gets a little weaker at the bending point until suddenly, it breaks.

 

[nhmoose]

Perhaps the nipple got cross thread the last time replaced?

Many questions on it IMHO. To much to understand as standard here.

 

[Britsmoothy]

His luck.
Actually, things had been changing with each shot.

Repeatedly subjecting a material to high stresses will lead to failure of the part. It's called fatigue, in this case, "low cycle fatigue".
It's like bending something back and forth a number of times. Each time, it gets a little weaker at the bending point until suddenly, it breaks.

Ummm.
Historian previously mentioned the importance of using a suitable wad with loading steel shot.
Was not this load using a suitable wad for steel?

One minute it is important to use a steel safe wad and the next moment a nipple blew out whilst using a steel safe wad!
How do we rule out human error else where?
If we can't rule out an error elsewhere how do we assume this failure is down to the steel shot?

If as you suggest Zonie, a low cycle failure would not the nipple been growing in length or lifting off its seat?

Could not yet another charge of anecdotal assuming be leveled at this scenario and thus it be accused itself of not being evidence?

Surely, if steel shot was an internationally known danger when used in muzzleloaders would not the industry condemn its use in clear no nonsense language?

B.

 

[Zonie]

I was just answering your question.
Without knowing the condition of the nipple and the nipple threads in the barrel before the event happened I don't know what the actual cause of the failure was.

I am guessing the threads were damaged before the failure because even with the higher pressures caused by using steel shot, the nipple is not really subjected to a lot of force when the gun fires.

For instance, if the nipple was using a 1/4-28 thread, its effective area would be 0.0491 square inches. At 10,000 psi breech pressure the force on the nipple that is trying to blow it out of the hole would be 10,000 X .0491 = 490.087 pounds.
A 1/4-28 screw made out of low carbon steel can safely exert a clamping load of 1,500 clamping load or, 3 times the load that 10,000 psi breech pressure would exert on it.

If the nipple thread size was a 5/16-24, its effective surface area would be .0767 square inches. This area times 10,000 psi breech pressure would create a load of 766.99 pounds. A 5/16-24 thread made out of low carbon steel can safely exert a clamp load of 2395 pounds or 3 times the load firing the gun would create.

Now, some of that extra loading the threads can take will be used up when the nipple is tightened as tightening it is just creating a clamp load between the nipple and the nipple seat on the barrel or drum but, even if the nipple was excessively tightened before the gun was fired, I would think there would be at least a safety factor of at least 1.

By the way folks, the fact that the screw has a limited load carrying capability and tightening the screw uses up some of it leaving what ever is left to do the job of keeping the nipple from blowing out when the gun is fired is a good reason why you should not tighten a nipple too tight. If you used a torque of 4 foot pounds to tighten the 1/4-28 nipple you will have used up most of the strength in the threads just by tightening the nipple. That doesn't leave a lot of strength to withstand the breech pressure when the gun fires.

Just seat the nipple out and then give it a nice "tighter than snug" tightening.

 

[Britsmoothy]

I was just answering your question.
Without knowing the condition of the nipple and the nipple threads in the barrel before the event happened I don't know what the actual cause of the failure was.

I am guessing the threads were damaged before the failure because even with the higher pressures caused by using steel shot, the nipple is not really subjected to a lot of force when the gun fires.

For instance, if the nipple was using a 1/4-28 thread, its effective area would be 0.0491 square inches. At 10,000 psi breech pressure the force on the nipple that is trying to blow it out of the hole would be 10,000 X .0491 = 490.087 pounds.
A 1/4-28 screw made out of low carbon steel can safely exert a clamping load of 1,500 clamping load or, 3 times the load that 10,000 psi breech pressure would exert on it.

If the nipple thread size was a 5/16-24, its effective surface area would be .0767 square inches. This area times 10,000 psi breech pressure would create a load of 766.99 pounds. A 5/16-24 thread made out of low carbon steel can safely exert a clamp load of 2395 pounds or 3 times the load firing the gun would create.

Now, some of that extra loading the threads can take will be used up when the nipple is tightened as tightening it is just creating a clamp load between the nipple and the nipple seat on the barrel or drum but, even if the nipple was excessively tightened before the gun was fired, I would think there would be at least a safety factor of at least 1.

By the way folks, the fact that the screw has a limited load carrying capability and tightening the screw uses up some of it leaving what ever is left to do the job of keeping the nipple from blowing out when the gun is fired is a good reason why you should not tighten a nipple too tight. If you used a torque of 4 foot pounds to tighten the 1/4-28 nipple you will have used up most of the strength in the threads just by tightening the nipple. That doesn't leave a lot of strength to withstand the breech pressure when the gun fires.

Just seat the nipple out and then give it a nice "tighter than snug" tightening.

Excellent Zonie.
Those are the facts.
Thank you.

Looks like the possibility for Historians nipple failure other than steel shot may exist or at this time can not be ruled out.

B.

 

[Bo T]

Zonie,
Wouldn't the pressure exerted on the nipple be proportional to the area of the nipple inside the chamber irrespective of the thread size? Also, I don't understand the effect of torque on the threads. I can visualize the vectors, but don't know how ft-lb relates to psi.

 

[Zonie]

Zonie,
Wouldn't the pressure exerted on the nipple be proportional to the area of the nipple inside the chamber irrespective of the thread size? Also, I don't understand the effect of torque on the threads. I can visualize the vectors, but don't know how ft-lb relates to psi.

Your right. The pressure on the nipple is directly proportional to the area of the nipple that is exposed to the pressure but the area of interest that is creating a thrust in the direction that would blow the nipple out of the hole is only acting on the surfaces that block off the threaded hole. The thread is that area so I used the major diameter of the thread to calculate the surface area. (Yes, my answer is slightly larger than the actual threads area is because between the major diameter of the thread and the minor diameter, only half of the sealing surface is the nipples thread. The other half in this area that is not contributing to the force on the nipple is the thread in the gun.)

As for how torque effects things, the tighter the nipple (or screw) is tightened the more thrust in generates. Torque in the USA is measured in pound/feet or pound/inches although, most people in this country say it backwards so they say "foot-pound" or "inch-pound".

Regardless of what they call it, it is the twisting power that is made when a certain weight is applied at a certain distance from the axis of rotation. Think of a wrench on a bolt. If the wrench is 12 inches long and a force of 5 pounds is applied exactly at that spot it will develop a torque of 12 inches X 5 pounds or, 60 "inch pounds". If we are talking in feet it would be 1 foot X 5 pounds = 5 "ft/lbs".

Getting back to the idea that more torque makes the thread apply more force there are several formulas for figuring out what the answer for any thread at any force would create.
One of the more common formulas is: L = T/(DK) where L is the load in pounds, T is the torque in inch pounds, D is the thread major diamter and K is a constant. Written out this would be, Load = Torque in inch pounds divided by (Diameter of thread times a constant number) = Force in pounds.

Oddly, the force doesn't have any thing to do with the number of threads per inch. It does have a lot do do with whether the threads are dry, steel on steel or, lubricated steel on steel and this is K, the constant.

The constant for dry steel threads is 0.20 The constant for lubricated steel threads is 0.15

Let's look at the load I mentioned above that is made when a torque of 4 ft/lbs is applied to a dry 1/4 inch thread.
4 ft/lb X 12 = 48 inch pounds so we have: 48/(.250 X .20) = 48/.050 = 960 pounds.

If the threads were lubricated with oil, grease or even a anti-seize compound, the force would be 48/(.250 X .15) = 48/.0375 = 1280 pounds.

(For what it's worth, in the calculation I mentioned in my previous post up above I assumed the threads would be lubricated with something and a ballpark maximum load for a low carbon steel 1/4" thread is about 1350 pounds. 1350 pounds minus 1280 pounds leaves 70 pounds of strength left to take the 767 pound load produced by the 10,000 psi breech pressure.)

Hopefully, all this calculating didn't confuse too many of you folks.

 

[smo]

Historian For what it’s worth....

The 2 ozs of bb's that started the quagmire was shot from a Flintlock not a perc gun.

The Flintlock touch hole has been enlarged... a lot.
I don’t recall the size right off , could be 1/16 th” or maybe even 1/8”.
I still have the gun and can verify if need be.

When shooting fffg , when ramming the ball home a good amount of powder sprays out the touch hole, but not enough to self prime the gun. Dang it! LOL

I don’t think in my case there is any concern with over pressure due too the size of the vent , even shooting the 2 oz load of bb’s which is equal to 3 ozs of lead..... per your post above.


Here’s a question for you.

When you blew the nipple out, did you just screw another one back in or did you have too chase the threads?

I’ve done the same thing in the past.
I had too chase mine, they weren’t completely stripped but slightly buggered up.

It did knock the hammer back to full cock but didn’t do any other damage to the gun or myself.

The reason it blew was the nipple was ONLY finger tight was yours tight?

Was it the original nipple or had it been replaced?

If so was it the correct size ?