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!

[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!