Secondary Pressures...

[geraldbergeron]

First time I hear about "Secondary Pressures" in internal ballistic...

It seems that a second "bang" can happen inside the barrel...

WOW

"In every instance when secondary pressures are detected they can be eliminated by using a faster power, heavier bullet or a bullet with more bore contact area. Normal "tweaking" of loads may change the peak of secondary pressures but will not eliminate the problem. Below is the list of factors we now know can cause secondary pressures.

Powder burn rate too slow for the bullet.
Bullet weight too light for the powder's burn rate.
Bullet bore contact area less then normal for the bullet weight
Barrel longer then normal
Bore severely worn or incorrectly lapped (loose/worn toward the muzzle)
Moly in bore or moly coated bullets that reduce bore friction "

http://www.shootingsoftware.com/barrel.htm


Question:

Have you heard of secondary pression inside a rifle barrel ?

Is it a true phenomenon or a theoretical thing ?

Is it possible inside a sm10-II ?? ($100,000.00 Can Question...)

May be just one individual... lived that ??

What do you think ?

..........................................................Gerald............../

 

[Anonymous]

Is it a true phenomenon ?

According the senior ballisticians at Accurate Arms and ATK-- it cannot happen. It is called just a "bad pressure curve."
:shock: :shock: :shock:

How many bangs are you supposed to hear?

 

[geraldbergeron]

According the senior ballisticians at Accurate Arms and ATK-- it cannot happen. It is called just a "bad pressure curve."
:shock: :shock: :shock:

And according to YOU... do you think it can happen ? What is your experience ?

Thank you........................................................Gerald................../

 

[Tar-12]

Gerald, You better stop that deer a running,I am getting ready to shoot him! :lol:

 

[Anonymous]

Not plausible. The attempt at a curve above is way off the map-- the .223 Remington has a 55,000 PSI SAAMI limit.

Ball powder burns in almost a completely regressive state.

What it does show is the potential unreliability of strain gage systems vs. the direct pressure reading of radial transducers. No ammo maker or powder maker I know wastes their time with cheap RSI software that can give bizarre results like that.

Dedicated pressure barrels are very expensive, and for reliable readings the transducers are calibrated, and cleaned after every single shot. Accurate Arms uses DUAL radial tranducers on top of that, DIRECTLY measuring the pressure TWICE with every shot.

Plastic glued strain gages are useful, but unreliable in muzzleloading compared to taking pressure measurements directly. They do not pressure, they measure "micro-strain." Micro-strain is converted to a number, but it is just a number. Dr. Oehler uses a 7000 psi offset to get get reading close in cartridges. You can fire factory SAAMI ammo, and compare it to your reloads. It cannot give you an exact pressure-- all it can do is tell you if your reloads are relatively higher or lower than a factory load-- that's all. No strain gage is considered particularly useful without a calibration load. With the 10ML-II, there is NO such thing as a calibration load.

A strain gage measures temporary stretch, actually. A big issue with muzzleloader is that rather than having a calibration load and a fixed cartridge length, the "caseless cartridge" can have infinitely variable lengths. Where do you put the strain gage?

Piezo radial tranducers, measuring pressure directly, are miles ahead of plastic glued strain gages in muzzleloading-- that never see pressure directly, and cannot be precisely calibrated. A bad, worthless curve is easy to find with a strain gage-- not so with direct, dual, redundant pressure measurement.

It is the difference between using tire deflection to guess at pressure, and precisely measuring actual air pressure through the valve stem.

That's a thumbnail sketch. There is no reason to buy into such ridiculous bunk when professional ballisticians that burn more powder in a week than any of us will in our lifetimes have volumes of directly measured pressure testing that refutes this.

 

[savagebrother]

so randy, where do you put the peizo's, there is still no cartridge to put them against. where on the pressure barrel do you locate the peizo's for a given load and sabot/bullet combo. i think we all know the answer, at the breech end and yes you can have a second pressure spike, especially when someone gets a hang fire or a delayed discharge. under normal conditions you wont. i found that if the head space is bad-meaning its to big you definitlly will get to pressure spikes in a cartridge gun.
if some one fires there savage and gets a missfire but fails to re-seat the bullet sabot they may get the same condition and cause a barrel buldge, usually a inch or two in front of the breech plug.
sb

 

[Anonymous]

A secondary pressure curve is physically impossible.

Johan Loubser, for example, has been a professional ballistician for 26 years, burning more powder in a week than most will in their entire lives. In all these 26 years of developing, testing, and designing powders and loads, all these years of using dedicated pressure guns, he has never seen a single "second pressure curve." It has never happened, cannot, and no professional ballistician has ever documented one-- from Western Powders, ATK, Hodgdon, etc., to Hartmut Broemel.

 

[Blue-Dot-37.5]

Randy:

I've learned never to say never. :wink: What about if the rifle barrel was "choked" at the muzzle end? Wouldn't the tighter constriction cause increased drag on the bullet, causing the pressure to rise enough to force it past the constriction?

Blue-Dot-37.5

 

[Anonymous]

Like shooting a foster slug through a full choke?

Sure, never is a very long time-- when the top ballisticians in the world unanimously say it is not a possibility, and that they have never recorded it in hundreds of thousands of laboratory tests-- I'm not going to strongly "hope" for it. There may be a Loch Ness monster as well.

 

[Blue-Dot-37.5]

I was thinking more along the lines of a .22 lr, but your scenario will do!

We have used the strain guages at work on truck chassis to see how much they are flexing. We know what type of steel, and how thick, so we can tell if that particular joint will fail prematurely. We still do a full blown durability test of the whole truck, but this gives us a good indicator if it'll make it thru the test without falling apart.

Blue-Dot-37.5

 

[Rifleman]

Yeah , well I would have made it through college too, if it had not been for my horse! :shock:

 

[Doohan]

lol!

Lewis Black is a funny guy!

 

[savagebrother]

well for one thing randy, ballistians are looking for good loads not bad. there job is to develope loads that work and are safe. so to say that they have never seen a secondary spike doesnt surprise me at all. i dont think you would ever see one under perfect conditions, which is what most of them work under. now lets talk about a forensic engineer-his job is to see why something went wrong and determine why. he may test something to destruction just to see if it would go as far as they said it would. he is working with items in the real world, under not so perfect conditions.
now if a safe load were loaded into a savage and its a factory load at that, and then when fired the owner notices a bulged area near the breech plug, what caused this to happen. in talking with a few people most were happening with a hang fire. what is a hang fire?? well it seems to me that it would be a partial ignition followed by a complete ignition after a few milliseconds or so. were we building pressure?? of course powder is burning therefore we have to have pressure, not a full pressure but enough to maintain a burn. now we have a big space between the sabot/bullet and the breech plug. when the main part of the powder ignites and pressures increase to normal where does it go?? two directions-toward the breech plug and towards the muzzle. problem is when it hits the breech plug it has no where else to go-second and damaging pressure spike now occurs because the sabot/bullet can only move so fast but not fast enough to clear the pressure being created by the now full pressure burn of the powder. remember this is a pressure wave or shock wave and when it hits something, something has to give. end result-a bulged barrel just ahead of the breech plug.
sb

 

[Anonymous]

Do you have any idea of what the "shot-start" pressure of a sabot is?

 

[Underclocked]

Have you ever crapped your pants, thought it was over, and 30 seconds later here it comes again!?

Never based upon inductive logic will dirty your shorts everytime. Why is it physically impossible? What is detonation? Why is the sky generally blue (still in some few places)?

 

[dwhunter]

Have you ever crapped your pants, thought it was over, and 30 seconds later here it comes again!?

Never based upon inductive logic will dirty your shorts everytime. Why is it physically impossible? What is detonation? Why is the sky generally blue (still in some few places)?

:lol: :lol: :lol: :lol:

 

[savagebrother]

its not much randy, but i am sure you have found someone thats measured it. but anyway, that has been our problem with pressure starved loads. thats why 70 grains of h or imr-4198 work better than 40 grains. we have to maintain enough pressure to make the smokeless burn consistently. i said this 4 years ago-we will have to always use a big load of slow powder in smokeless muzzleloaders to go fast, that has proven to be correct, also a longer barrel, that has proven to be true too.
nothing agianst present design, it works well and fits the bill for most.
sb

 

[savagebrother]

its not much randy, but i am sure you have found someone thats measured it. but anyway, that has been our problem with pressure starved loads. thats why 70 grains of h or imr-4198 work better than 40 grains. we have to maintain enough pressure to make the smokeless burn consistently. i said this 4 years ago-we will have to always use a big load of slow powder in smokeless muzzleloaders to go fast, that has proven to be correct, also a longer barrel, that has proven to be true too.
nothing agianst present design, it works well and fits the bill for most.
sb

 

[Anonymous]

Have you ever . . . ?

And that's why fire engines are red.

 

[Rifleman]

Just a note to all those timid souls that read this but are too smart to comment on an issue such as this. If your corn-fused don't feel bad. I have been shooting for 38 years, teaching shooting for about 28 years now, reloaded for about 22 years loading well over 150,000 rounds, am considered to be well read on the subject of ballistics and I still don't know FOR SURE what the right answer here is!
Think I will just leave it out there in the unanswered questions of life realm for now and go eat some pie. :wink: