Stopped bullet

[DickE]

OK, since there was such a nice discussion on recoil, I thought I'd throw in another good one. How many times does a bullet stop in the chamber/barrel, once the firing pin hits the primer? Give me proof one way or the other.

 

[Preacher]

I'll assume that if the case has powder in it, when the firing pin hits the primer and sends the bullet on it's way it never stops until it hits what your aiming at

 

[SooStan]

I have heard that it starts and stops twice but as far as proof, you got me on that one. I don't really know.

 

[gunsandgunsmithing]

I'm with Preacher. My Pressure Trace can prove it.---Mike Ezell

 

[DickE]

look at http://longrangehunting.com/articles/happens-fire-gun-1.php
and http://www.snipercountry.com/Articles/Barrel_BreakIn_II.asp

 

[6BRonwheels]

I am also going to side with Preacher. There are a lot of articles out there that are not worth the paper they are written on. I just read an article that touted the 243 WSSM as a great sniper cartridge, and another article saying that the 308 Winchester is 50% more accurate than the 30-06. I have to disagree with both those articles, just my uneducated opinion.

 

[Akbushape]

If the bullet stops it would have to be as it first moved out
and wedged into the lands during the very begining of the
powder explosion. This could only be for a fraction of a milisecond and the bullet would move again as pressure buids behind it. I could maybe buy this scenario. Once the bullet was
formed to the rifleing and started moving a second time I would
have a hard time believing it would stop again. But what do I
know. Uhh..Don't think I'll try a quick peek to see. Where's
the rocket scientist?

 

[Preacher]

What happens when the bullet is into the lands when it's loaded, I doubt it would be moved by the primer blast, or the initial powder blast......

 

[Akbushape]

What happens when the bullets are into the lands?

Is this a trick question preacher? What kind of neck crimp are
you putting on your loads?
You can load a round against the lands but unless you crimp the
neck more than you can with any die I ever used you won't force
the bullet into the lands. Provided you could crimp it that well, to get the bolt to close you would have to whang on the
bolt handle a few times with a stick of stove wood.,That would be noisy and scare off the little animals, besides who wants to pack around a stick of stove wood?) Nope, don't believe you can load a round into the lands. After reading your other post
I have to assume you are playing the devil's advocate. If
you're not stirring up hate and discontent here then please explain what I missed. ,I'm no rocket scientist but sometimes I
have to be showed if something don't line up with common sense or common logic.)

 

[Akbushape]

I agree with what you said gunamonth. The difference is what you stated just kind of dents the bullet at the ogive and it
doesn't take a lot of pressure to do that. To leave a signficant crease in the bullet to the extent that it would take
to prevent,possibly) a "jump-stop" of the bullet would require
most or all of the rifling to be cut in the bullet at the start. Which isn't possible when the bullet is seated in the neck. Just seating against the lands does't seem like it would change things much.,I'm not explaining this very well)
Still looking for the rocket scientist. I've heard of this start-stop phenomenon before but never seen the proof or had it
explained.

 

[Preacher]

Well the only time I put out hate and discontent was with the ex wifes
Some folks jam the bullet up to .020 into the lands and they will shoot way
better than if they are jumped to the lands....
Some bullets like it some don't, and thats where the fun begins......
Sometimes it will increase pressure, but so will a bullet to far into a case.
Just more fun to deal with again......

 

[SooStan]

"I'm with Preacher. My Pressure Trace can prove it.---Mike Ezell"

Not that I disagree but how much pressure does it take to move a bullet once it is in the bore? Only then would the pressure curve show if it was moving.

 

[DickE]

Does anyone know Mike Rock? Or does anyone do business with Rock Creek Barrels? Their web site and gallery makes one believe they know what they are doing. Mike is the one quoted as doing some of the studying on this bullet stopping question.

 

[Akbushape]

Thanks for sharing those web sites DickE. The article at long range hunting is worth the read. There's a lot more food for thought in it than just what the bullet does.

 

[glo]

Hi Guys,
I just did a little simple math. All things being equal, if a bullet is set off the lands ten thousandths of an inch,.010”) the time it takes to meet the lands is 16 millionths of a second,.000016sec.). I think that’s pretty good mathematical evidence that a bullet doesn’t start and then stop again. I could see the bullet slowing down for the pressure to build. That should show up as a dip in the pressure curve. I’ve see lots of those. But, a bullet completely stop? That’s called, blowed-up-gun. I would love to see what gunsandgunsmithing’s pressure trace read-out’s show within the pressure curve.

If there is enough interest within the membership, I would be willing,within the wife’s budget) to do some pressure testing and post the results. Given enough interest I’ll even purposely cause a bullet to stop in barrel using a light bullet and slow powder.

That didn't make too much sence did it. I'll figure out how the express the math in better english later.

 

[glo]

I’m not a rocket scientist. That was my father’s profession. But here’s the common explanation of the bullet start and stop phenomenon. The phenomenon you are referring to was a problem within the hand loading community for many years and was not proven until a Swedish firm did the testing about 15 years ago. This phenomenon manifested itself when slow powder was used in conjunction with light bullets in cartridges like the .25-06’.

This firm as I recall used a 6.5x55mm as its test cartridge. Here is what happened. The slow powder had enough built up pressure to get the light bullet moving. This is called overcoming inertia. However, as the pressure dropped the bullet slowed down and wedged up in the barrel. Then the pressure built up again behind the now stopped bullet and BOOM. The barrel splits down the side and the bolt lugs sheer off resulting in catastrophic failure of the firearm. In structural engineering this is called exceeding the plastic limits of design.

So why dose the pressure build up then go down then build up again?

I’m glad you asked

Smokeless powder is a propellant. It is designed too deflagrate,subsonic burn) at normal atmospheric pressure and detonate,supersonic burn) under pressure. This engineered burning rate is specific to the structural parameters of any given firearm cartridge. All smokeless powders are capably of creating inexcess of 100,000psi pressures.

What keeps pressures from exceeding a more normal 55,000 to 60,000psi range for the modern bottle neck rifle cartridge? That my friends is the listed reload by the reloading component manufacture with all the warnings such as, “ALWAYS USE THE LISTED COMPONENTS AND NEVER EXCEED THE LOADS WITHIN THIS RELOADERS GUIDE.”

You can if you wish damage any firearm at anytime by using the wrong listed powder. It takes no scientific testing, proof, or peer review papers to be stupid.

So what will happen if you load a .308 Winchester cartridge with a full case of H50BMG powder and top it off with a 110gr bullet? The bullet is light and its inertia will easily be overcome. The bullet will be punched way out in front of the powder's designed detonation rate. Because the bullet is way in front of the pressure curve, the bullet must slow down until pressure back builds up again.Technically this slowdown is known as d/t^2; deceleration,also acceleration when speeding up)
1) If the bullet slows down a little the pressure will build back up behind the bullet as the burning rate catches up with the bullet's movement. You will see a drop in the pressure curve. When the pressure builds back up the bullet can still safely exit the barrel.
2) If the bullet slows down a little too much the pressure will still build back up behind the bullet as the burning rate catches up with the bullet's movement. You will also see a drop in the pressure curve and there will be an extreme spike in pressure. This will stress the structural integrity of the firearm. The bullet can still safely exit the barrel.
3) If the bullet slows down and stops due to lack of pressure, the pressure will still build back up behind the bullet as the burning rate catches up with now stopped bullet. You now see an end to any pressure curve. All of the newly built up pressure will hit the base of the bullet and swage it in the barrel. There will be a failure in the firearm. The bullet never safely exits the barrel. You can not overcome inertia in an instant. Technically instant start up is known as d/t^3; jerk. But I'll arguee the "jerk" with any mechanical engineer,inother words the "jerk" is a load of crap).

 

[Akbushape]

So I gether from what I have read here and elsewhere that a
bullet will not start/stop if every thing about the gun and the round is as it should be, right type of powder in the right size
case with the right size bullet in a properly machined chamber
with the proper headspace using the proper primer with the proper neck tension.,thats a heck of a lot of places for error).
If all these components are not correct then start/stop once or
even twice may occur. And if things are way off you can have the
bullet stop farther out the barrel and blow the gun up.
It seems to me after the throat burns out in a barrel the chances of the stop phenomenon occuring would be greater than in
a new barrel, since the tolerances would deteriorate.
Glo, if the bullet jumps at primer detonation there would be a lot of factors at play so I don't see how a fixed number like
15 millionths of a second could be applied. It seems to me it could range from slowing slightly to an actual stop as has been
claimed by some test.
Another thought,I know, I think to much), but seating the bullet against the lands and getting improved accuracy as a
result may serve the purpose of preventing the S/S from occuring, or not?

 

[glo]

Akbushape, as I added a bit later in my previous post, the 16 millionths number was not well written. I’ve been thinking of how to better write what I understand.

As I understand the whole detonation process, primer detonation dose not force the powder column up into the bullet causing the bullet to jump. Then the powder begins to burn creating pressure the gets the bullet moving again. I understand the process as being: The detonation of the primer and the detonation of the powder column and resulting energy transfer happens way faster then it takes the bullet to move ten thousandths of an inch to the lands. That is it takes the primer and powder detonation to occur in about 16 millionths of a second and it takes the bullet a lot longer to travel the ten thousandths of an inch.

When I have time I’ll run the numbers and figure out the correct acceleration for the bullet at rest in the cartridge and then the subsequent ten thousandths of an inch to the lands. I think that distance will translate into a time frame of around .001 seconds or about 100 times slower than the primer/powder detonation acceleration.

I think you already understand how bullet jump affects accuracy. That’s a subject I need lean about from other more informed shooters. I think the bench rest guys are the most knowledgeable about that subject.
G

 

[Akbushape]

A magnum pistol primer seated in an empty 44 case will shoot a
plastic bullet with enough velocity to punch a hole through a cabela's reloading catalog,about 100 pages) at about 10 feet. That's just the primer and no powder.
I've never tried it but am sure a primer alone would jam a rifle bullet well into the barrel. Having powder in the case
would drastically buffer the impact from the primer explosion
to prevent the bullet from jumping well into the lands as the
primer explodes. Still it seems logical that enough pressure could be produced to jump the bullet some. How much if any would depend on all the factors previously listed.
I totally understand that the primer explosion, powder ignition
and movement of the bullet all occurs in a matter of nanoseconds.
So what's happening? Are those who have tested bullet stop and
claim that it happens feeding us a line of BS? Or is it real.
Does it happen always? Sometime? Never? Seems like there is
room for someone with the means and equipment to do a lot more
studying on this especially with the effect it could have on
rifle accuracy. It may not be a matter of life and death to a
bench shooter but it could be to a military sniper.

 

[glo]

I don’t know if anyone is trying to feed us a line of BS. I know that from an engineering stand point that if indeed the bullet dose start then stop again its inconsequential. Therefore the engineering community has ignored this phenomenon and moved on to other things. This leaves us the public wondering what’s going on. I for one don’t know where this S/S thing started for as it pertains to initial primer ignition exclusive of powder charge ignition.

Maybe S/S is real and happens at the micro level, where ten thousandths of an inch is like a mile and a microsecond is like a week. From that point of observation a lot can happen in a short period of time. Personally I think it’s a crock because it violate F=ma for properly functioning firearms.

ADDED: I just graphed the pressure curve that’s on the Southwest Products web page for the Pressure Trace II. It appears that within .0000225 seconds,22.5 microseconds) the pressure is already about 12,000psi. And by making a wild guess using Le Duc’s Equation the peak pressure happens about 3.7 inch of bullet travel. So, the 12,000psi happens,again a guess) at about .014 inches,fourteen thousandths of an inch)of bullet travel.

That’s just about the ten thousandths of an inch, bullet jump we have been discussing. I guess we now have to test primer pressure to see if a primer can develop 12,000psi or there about.

I will talk to my wife about getting a Pressure trace II from southwest products http://www.swproducts.biz/ If she goes for it, I’ll put off counter sniper rifle project and do some testing to see what gives.