More on Bullet Setback

[muggsy]

Found this article that I thought would be of interest concerning bullet set back experiments.

https://plus.google.com/+luckygunner/posts/CiVxdHvWjYS

[RRP]

Interesting read. Thanks for the info.

[muggsy]

While bullet set back does have a detrimental effect on accuracy it doesn't set up the gun for a catastrophic failure. When a gun is fired the case expands to fill and seal the chamber. The expansion of the case releases the bullet to travel down the barrel. The bullet obturates to fill and seal the bore. With bullet setback the pressure may peak sooner, but the same amount of pressure expands the case and releases the bullet. I have never seen one documented case where bullet set back was determined to have caused a catastrophic failure of a firearm.

[knkali]

Thanks Muggs. makes sense when you think about it. I now have about 100 rnds of 5.56 NATO that I have rat holed away because I thought I might have bullet setback. I was saving it as last resort stock. I think I will use it as range ammo now with peace of mind.

[downtownv]

I one time feared that issue only to find like what you said it was a non issue. My mistake was comparing my load to a factory load on overall length.

[jocko]

MUGGSY;;;"obturates".

WTf.u canget banned for using that kind of languageon this forum. Its a family forum. Just sayin

[RevRay]

MUGGSY;;;"obturates".

WTf.u canget banned for using that kind of languageon this forum. Its a family forum. Just sayin

Definition of Obturate according to Dictionary.com ... to close (a hole or cavity) so as to prevent a flow of gas through it, especially the escape of explosive gas from a gun tube during firing.

Origin: 1550–60; < L obtūrātus, ptp. of obtūrāre to block, stop up.

I don't think Muggsey should get banned from the forum for using a gun-related term that's been around since the 1500's.

Jocko, you're a Princeton professor ... you should know better ... just saying.

[muggsy]

Jocko is enitled to his opinion, Rev Ray, no matter how absurd it may be. We still temporarily live in a free country. :)

[micotu]

While bullet set back does have a detrimental effect on accuracy it doesn't set up the gun for a catastrophic failure. When a gun is fired the case expands to fill and seal the chamber. The expansion of the case releases the bullet to travel down the barrel. The bullet obturates to fill and seal the bore. With bullet setback the pressure may peak sooner, but the same amount of pressure expands the case and releases the bullet. I have never seen one documented case where bullet set back was determined to have caused a catastrophic failure of a firearm.

From my background as a physics major. The ideal gas law follows the formula PV=nRT where P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of gas or essential how many atoms of the gas (in moles), T is the temperature of the gas and R is a constant that is the same for all equations.

If we look at a normal bullet and a setback bullet, we have to analyze the gas immediately after the explosion. For both cases the n will stay the same because there are the same number of atoms in the casing. T will also be the same because the temperature of the gas after the explosion should stay roughly the same. R will be the same because it is a constant.

That leaves us with P and V. When bullet setback occurs, the volume of the case is decreased. So for P x V to still equal nRT, as V goes down, P must go up. So in other words, as the volume of the case decreases due to bullet setback, the pressure of the explosion will increase, causing potential damage to your firearm.

[MW surveyor]

I just caint belive someone from Mississippi had to explane the math! j/k

(and the spellin mistakes are intentional!)

[muggsy]

Thanks Muggs. makes sense when you think about it. I now have about 100 rnds of 5.56 NATO that I have rat holed away because I thought I might have bullet setback. I was saving it as last resort stock. I think I will use it as range ammo now with peace of mind.

I don't know if the same holds true for rifle ammo. I do know that if you don't seat rifle bullets deep enough and they touch the rifling that it takes more pressure to start them down the barrel. Seat them too deeply and accuracy is adversely affected. When in doubt err on the side of caution. If they aren't set back more than .025 I'd shoot them.

[micotu]

I just caint belive someone from Mississippi had to explane the math! j/k

(and the spellin mistakes are intentional!)

We're not all backwoods hicks in Mississippi. I got the brains, but my sister got the beauty. She's a damn good kisser too.

[sas PM9]

From my background as a physics major. The ideal gas law follows the formula PV=nRT where P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of gas or essential how many atoms of the gas (in moles), T is the temperature of the gas and R is a constant that is the same for all equations.

If we look at a normal bullet and a setback bullet, we have to analyze the gas immediately after the explosion. For both cases the n will stay the same because there are the same number of atoms in the casing. T will also be the same because the temperature of the gas after the explosion should stay roughly the same. R will be the same because it is a constant.

That leaves us with P and V. When bullet setback occurs, the volume of the case is decreased. So for P x V to still equal nRT, as V goes down, P must go up. So in other words, as the volume of the case decreases due to bullet setback, the pressure of the explosion will increase, causing potential damage to your firearm.


+1000, What he said.

To illustrate this for us with a lesser physics background; I provide this info from the Speer reloading manual #10 on page 349 covering the reloading of 9mm Parabellum cartridges.

" loads that produced 28,000 c.u.p. went to 62,000 c.u.p. when the bullets were purposely seated .030" deeper! Thus it is of the utmost importance that bullets do not become deeper seated in the feeding cycle."

I don't know at what pressure your handgun ceases to be handgun and becomes a grenade, but I don't wish to test the theory.

HTH.

-steve

[MW surveyor]

We're not all backwoods hicks in Mississippi. I got the brains, but my sister got the beauty. She's a damn good kisser too.

ROFLMAO.

Just to be serious. I now know at least two people in Mississippi that be smart! :D

[downtownv]

Definition of Obturate according to Dictionary.com ... to close (a hole or cavity) so as to prevent a flow of gas through it, especially the escape of explosive gas from a gun tube during firing.

Origin: 1550–60; < L obtūrātus, ptp. of obtūrāre to block, stop up.

I don't think Muggsey should get banned from the forum for using a gun-related term that's been around since the 1500's.

Jocko, you're a Princeton professor ... you should know better ... just saying.

I think I'm guilty of that fill in cavity stuff some in countries that I am not sure of the legality there in the first place!:behindsofa:

[muggsy]

From my background as a physics major. The ideal gas law follows the formula PV=nRT where P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of gas or essential how many atoms of the gas (in moles), T is the temperature of the gas and R is a constant that is the same for all equations.

If we look at a normal bullet and a setback bullet, we have to analyze the gas immediately after the explosion. For both cases the n will stay the same because there are the same number of atoms in the casing. T will also be the same because the temperature of the gas after the explosion should stay roughly the same. R will be the same because it is a constant.

That leaves us with P and V. When bullet setback occurs, the volume of the case is decreased. So for P x V to still equal nRT, as V goes down, P must go up. So in other words, as the volume of the case decreases due to bullet setback, the pressure of the explosion will increase, causing potential damage to your firearm.

I believe that you are correct, but does the pressure go up enough to cause a problem. Secondly the powder doesn't explode. The powder burns. The powder is a propellant, not an explosive. With black powder the projectile has to be seated firmly on the powder or it detonates. Quite confusing isn't it? Like I said, I have never seen a documented case where bullet set back has definitively been determined to be the cause of the catastrophic failure of a handgun. You're free to look for one.

[muggsy]

We're not all backwoods hicks in Mississippi. I got the brains, but my sister got the beauty. She's a damn good kisser too.

I like a man with a sense of humor. :)

[knkali]

+1000, What he said.

To illustrate this for us with a lesser physics background; I provide this info from the Speer reloading manual #10 on page 349 covering the reloading of 9mm Parabellum cartridges.

" loads that produced 28,000 c.u.p. went to 62,000 c.u.p. when the bullets were purposely seated .030" deeper! Thus it is of the utmost importance that bullets do not become deeper seated in the feeding cycle."

I don't know at what pressure your handgun ceases to be handgun and becomes a grenade, but I don't wish to test the theory.

HTH.

-steve

wow pressure doubles

[knkali]

From my background as a physics major. The ideal gas law follows the formula PV=nRT where P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of gas or essential how many atoms of the gas (in moles), T is the temperature of the gas and R is a constant that is the same for all equations.

If we look at a normal bullet and a setback bullet, we have to analyze the gas immediately after the explosion. For both cases the n will stay the same because there are the same number of atoms in the casing. T will also be the same because the temperature of the gas after the explosion should stay roughly the same. R will be the same because it is a constant.

That leaves us with P and V. When bullet setback occurs, the volume of the case is decreased. So for P x V to still equal nRT, as V goes down, P must go up. So in other words, as the volume of the case decreases due to bullet setback, the pressure of the explosion will increase, causing potential damage to your firearm.

I disagree. T will go up more than you think.

[muggsy]

The OAL of a 110 gr 9mm projectile is .470. The OAL of a 124 Gr. 9mm projectile is 590. If both bullets are seated to the max length of for 9mm cartridge the 124 gr projectile is "set back" .120 more than the 110 gr. projectile. I don't even want to contemplate how much a 147 gr. projectile might be "set back". I'm still waiting for someone to post a link to a study that proves definitively that bullet set back caused a catastrophic failure of a handgun.

[Gringo Pistolero]

The OAL of a 110 gr 9mm projectile is .470. The OAL of a 124 Gr. 9mm projectile is 590. If both bullets are seated to the max length of for 9mm cartridge the 124 gr projectile is "set back" .120 more than the 110 gr. projectile. I don't even want to contemplate how much a 147 gr. projectile might be "set back". I'm still waiting for someone to post a link to a study that proves definitively that bullet set back caused a catastrophic failure of a handgun.

That is true, but also completely irrelevant to the discussion of the dangers of bullet setback. In the case of different weight bullets, the powder charge is tailored to the projectile. Completely different situation.

I agree, though, that I have never heard of a documented case of bullet setback causing a catastrophic failure. Lots of speculation, but nothing conclusive.

[DKD]

Muggsy,

As an avid reloader I will try and explain your dilemma. Given the same powder being used in the heavier bullets in the same caliber...the powder grain charge weight will always go down as the bullet weight goes up. In a nut shell the case loading density remains the same only the case volume goes down as the bullet weight increases, thus the same over all case length doesn't change for a particular bullet. The bullet on heavier projectiles just get set a bit deeper in the case.
I hope this helps to explain the situation a little bit better.

[muggsy]

Muggsy,

As an avid reloader I will try and explain your dilemma. Given the same powder being used in the heavier bullets in the same caliber...the powder grain charge weight will always go down as the bullet weight goes up. In a nut shell the case loading density remains the same only the case volume goes down as the bullet weight increases, thus the same over all case length doesn't change for a particular bullet. The bullet on heavier projectiles just get set a bit deeper in the case.
I hope this helps to explain the situation a little bit better.

I too am an avid reloader and know that a charge of Red Dot takes up one hell of a lot less space than a charge of Unique, so the powder you choose has to be taken into consideration as well. My point being that I still haven't read one documented case where a gun suffered a catastrophic failure due to bullet set back. I'm going to offer a twenty dollar reward to the first person who can present one. I'll give you a month to find it. If after a month no one presents a documented case of catastrophic failure of a hand gun due to bullet setback you all owe me twenty dollars. Sound fair? :) (Got my bargaining skills from Bawanna.)

[jocko]

How about if Ol jocko just said he read it somewhere, would that suffice, as u know I would not lie and if it is on the internet it has to be the truth, so help me obumer

PM me and I will give u my mailing address-- cash only. Just sayin

[muggsy]

How about if Ol jocko just said he read it somewhere, would that suffice, as u know I would not lie and if it is on the internet it has to be the truth, so help me obumer

PM me and I will give u my mailing address-- cash only. Just sayin

If you're that desperate for money, I'll send you $20 you old reprobate. Bawanna will explain to you what a reprobate is. Just sayin. :)

[MW surveyor]

Muggsy, I here by and forth with nominate you to be our official tester on how much set back is too much.

First off, you need to load up some maximum powder ctgs and then set the bullets in increasing (or decreasing if your going by OAL) amounts. In order to make this a scientific experiment, say decrease the OAL by 0.001 until you can't compress the powder any more.

Second, fire them off in your favorite semi-auto.

Third, take note of which OAL blows-up the gun. (If gun does not blow-up, add more powder next time.)

Fourth, post results here so that we can say.........................you did it wrong!

LOL:)

[muggsy]

http://www.thegunzone.com/glock/setback.html

Yeah, those "Internet Myths" are are hard to kill. I remember reading about this particular incident in several places. Admittedly, there may be some truth in their assessment that a setback fotay round in an unsupported chamber poses some risk. http://home.mindspring.com/~justsomeguy/icon_lol.gif

From the picture of the barrel I say that a bore obstruction caused the failure. If an unsupported case fails the gas is vented to the rear and the barrel doesn't burst. The gun might be wrecked, but not the barrel itself. The chamber area is the strongest part of the barrel.