I have a question about bullet set back, reduced case capacity and pressures in a bottle neck rifle cartridge.

Lets say that I worked up a load with 25.2gr of Ramshot TAC, a 55gr Sierra SPT at 2.260in OAL for a 223 AR-15. Ramshot lists this load at 49,000psi.

What would happen to the pressures in a load like this if the bullet were to become severely set back during the cycling of the action? I guess what I am asking, is there enough pressure increase from bullet set back to have a catastrophic failure in a bottle neck cartridge?

Steve

You'd better believe it.

Get a copy of Ackley's Pocket Manual and read all about it on page 10.

Ray

Thanks Cheechako, I'll see if I can round up a copy.

I'm surprised that I received only one response to my question. I thought my question would have at least gotten my ass chewed once or twice.

I'm guessing that you're talking about some kind of accident that knocks the bullet into the neck resulting in very deep bullet seating? The pressure to a great extent depends upon the neck tension. If the neck tension was so light as to allow the bullet to be displaced that easily, I would not think there would be a blow up.

In BR shooting we load rounds like that but usually the neck tension id SO light we can pull the bullet back out again. I've done that a few times, but never fired the bullet as a score round afterward--- Not because of any pressure worries, but cocentricity issues.

Hey steve

I don't have PO Ackley's manual but it would seem like you would have the same amount of space in your chamber after the bullet was pushed forward to the lands. It is my understanding that it takes very little of the pressure to move the bullet to the lands whether crimped or not.

There are lots of instances of a large jump to the lands, like with Weatherby's, and no catastropic failures for that reason. Compressing the powder is commonly done and there are again no catastropic failures.

What would cause the problem?

I have quickload and it quickly adds pressure to a scenario as you seat the bullet deeper.
The idea is that the less room inside the case the faster the pressure builds. (I've heard people say the comparison is if you pumped a cubic foot of air into a tank that held 3/4 cf you would have pressure..if you pumped that same cubic foot into a tank that held 1/2 cf you'd have lots more pressure).
All that being said I've not seen nearly the pressure rises that QL predicts with seating depth. I guess a better comparison for us reloaders would be the fact that we all know that case capacity among the same cartridge can affect pressure....like in a 300 wby a rem case vrs a wby case....there is a noticeable difference usually. (And we can can do the same thing to case capacity by seating depth so to speak)
Bottom line....is I haven't played enough with it to substantiate a big swing one way or another but there is merit to the idea.
What I would recomend to you is to shoot that AR a bit and then pull a cartridge from the bottom of the clip that has moved.....and chrono it vrs's your first few firings.....then you'll know what effect it really has on your gun??

IMO, there is distinct difference in defining case capacity and combustion chamber volume. If you seat a bullet deeper and reduce the throat length so that the bullet does not have as far to go before hitting the lands, then you have increased pressure. If the throat length remains the same and you seat the bullet deeper then you still have the same size combustion chamber.

I see your point. I think you are saying that the bullet is basically gone out of the case before max pressure is made. According to a quick load pressure graph max pressure would be about an inch of bullet travel. So if you had a thick case lining the chamber of the rifle you would have less capacity in that chamber...thus the higher pressure.
Still....I wonder why quick load factors in pressure increases with deeper seating???

OK...hows this for an idea. If the bullet is seated deeper and max pressure is hit just after the bullet has left the case there is a smaller combustion chamber left behind BECAUSE the bullet hasn't travelled as far down the barrel as a bullet that was seated closer to the barrel in the first place?

Possible, but not how I envision it. The pressure needed to move the bullet is very small. The bullet almost immediately moves to the lands and then the pressure builds up. It takes that enormous amount of pressure to engrave the bullet into the lands and actually push it down the barrel. IMO the bullet is against the lands in all cases before the pressure builds to an amount large enough to push the bullet into the barrel.

For instance, in most cases you can put the bullet against a solid surface an push it further into the case. You might have to put some weight on it but you can move the bullet in the neck. Now try to push a bullet into the muzzle of a rifle. Better get a 3 pound sledge and get ready for some work!

So to my way of thinking the combustion chamber is from the bolt face down the chamber walls and all the way to the lands.

For example I have a 338 RUM that is a rebarrel of a 338 win mag. In order to be able to fit the magazine with the loaded 338RUM bullets I have to seat the bullets pretty deep. I had the gunsmith set the lands in close so I could reach the lands with a 225 gr Accubond and still fit the mag. I can not load that gun to the manual max because my combustion chamber is smaller than SAAMI spec. My primer pockets get loose if I load over 95 gr RL25.

Now the opposite would be true if I had a rifle that had a long leade (and a longer mag). I would be able to exceed manual max because my combustion chamber would be larger.

Does Quickload have a variable where you can set the bullet jump?

I understand what you are saying about different guns have different chambers and thus pressure. I guess what we've talked about doesn't have anything to do with the original post which is "does a deeper seated bullet increase pressure in the same rifle". I would envision the "combustion chamber" being the inside of the case because I would envision the case mouth pretty much closing off the rest of the chamber as the case expands? This would leave the inside of the case and whatever is inbetween the case and where the bullet is at max pressure.
Quickload doesn't have any factors for freebore or bullet jump....but it does increase pressure predictions for deeper seated bullets significantly.

quote:

Originally posted by
You'd better believe it.

I'm with Cheechako. I once negligently seated a batch of hornet bullets too deep. Not a lot mind you, but the pressure rise was astonishing! This doesn't mean it will always do that but it could.

There is another way of loking at it and that is that if the bullet is seated further back from the rifling, it might get a better start and enter the rifling quicker, thus tending to lower the pressure. But then again, a bullet that is forced into the case might well be sitting at an angle and worse still, might have a granule or two of powder wedging it in the neck. How far back does one expect a bullet to get rammed? Then too, what happens if the bullet that has been forced back into the case, gets moved forward quickly and stops on the rifling? That would surely cause a dangerous pressure rise as the pressure would be building up very quickly while the force required to engrave the bullet plus the bullet inertia would be accentuated!

Smokeless powder is a strange beast when in a confined space. When ignited, the charge starts to burn, creating pressure. As the pressure increases, it's burning rate increases exponetially. This is measured in Miliseconds, so it is damned quick.

A bullet, while easy to move in the neck under slowly applied pressure, is not so easy to move under a rapid application of pressure. Think of water... if I take my hand and slowly place it in the water, it goes in easily. But, drop me from 30 ft. in the air into the same water, and it is like hitting concrete.

Finally, there is a point in bullet seating depth where the base of the bullet does invade the chamber around the shoulder of the case. Seating it deaper does reduce chamber capacity, thus changing the burning rate of the smokeless powder charge. Hell, forget the bullet for a minute, and consider that the angle of the shoulder alone can change the burning rate of smokleless powder, and you can understand that seating depth, at some point, can start to increase pressure before the bullet starts to move.

That said, the pressures associated with freebore has a different effect. As I increase freebore (seating bullet deeper into the neck), it usually decreases pressure. This is due to the fact that the timing of the bullet engaging rifling as the chamber pressure is rising, again changes the burning rate of the powder. I also know that increasing freebore by as little as 5/1000's of an inch, can cause a very substantial reduction of velocity and accuracy.

My point?.... when trying to understand the mechanics of bullets, chambers, smokelss powder characteristics under pressure, and every other variable that we can introduce while reloading, it's pretty easy to get in over our heads.

The .223 is SAAMI registered at 55,000 psi, but a .223 case can be used a dozen times at 72,000 psi. But if the cartridge is loaded at 90,000 psi, the primer will fall out and the case can be only used once.

What does that mean?
Unlike the 308 and the 270, the .223 case has allot of safety margin.

50 years ago my father sold Detroit Arsenal a strain gauge system option for verifying that bullet was in the throat of the chamber. The Army was having trouble with bullets that went through the barrel crooked and when recovered, had rifling marks in the boat tail.

quote:

The .223 is SAAMI registered at 55,000 psi, but a .223 case can be used a dozen times at 72,000 psi. But if the cartridge is loaded at 90,000 psi, the primer will fall out and the case can be only used once.

Maybe, maybe not. My experience with 223 Rem, is that there are some powders that created high pressure and undesirable case distortion on the first loading, even when loaded according to listed loads below SAAMI max pressures. A load using IMR 3031 and 45 gr. Hornadys quickly comes to mind.

Each gun is an individual unto itself.

Undesirable case distortion is different for different hand loaders.

There are guys that load to short case life and back off a safety margin ala Vernon Speer 1958.

Then there are guys that say, "I have been loading for 50 years, and I had a primer pierce once...It was horrible!"

What does it all mean?
Mike, you right brained liberal, turn on the left hemisphere and define your terms.
This is not flower arranging for expressive dancers, this is metal with dimensions.

There is an small explanation of seating depth and how it affects pressure about 2/3 of the way down on the Hornady website.

quote:

To illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.

In a "normal" load with the bullet seated to allow about one 32nd of an inch gap (A) between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period (B), and the velocity obtained - 3500 fps - is "normal" for this load in this rifle.

Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start (C). Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps (D).

Essentially they are saying that seating a bullet deeper will decrease pressure. I do think that at some point the pressure will rise back up.

fwiw--just referenced my book from Stan Watson. It is a neat book to own called a handloaders odessy and he tests a couple 30-06's with all kinds of scenarios. Anyhow I checked his test on seating depth and found that there was little variance between seating a whopping .164" from the lands all the way to the lands. In his test with a 180 grain bullet the load .164 away from the lands did 2608fps at 50,600 psi.......at the lands it did 2622 at 52,100. He had several rounds in between the two I mentioned and pressure and speed was also between the two. Doesn't look like in this case anything amounted to much difference.
STILL TO THE ORIGINAL POSTER....I would say test for yourself with a deeper seated bullet and a regular one and see what happens IN YOUR GUN.

quote:

Originally posted by tnekkcc:
Undesirable case distortion is different for different hand loaders.

There are guys that load to short case life and back off a safety margin ala Vernon Speer 1958.

Then there are guys that say, "I have been loading for 50 years, and I had a primer pierce once...It was horrible!"

What does it all mean?
Mike, you right brained liberal, turn on the left hemisphere and define your terms.
This is not flower arranging for expressive dancers, this is metal with dimensions.

Tneck,

If you seriously like to discuss the 223 load with me, we could start a seperate thread. I have a picture and load information.

If you are concerned with the function of my brain, we could take that over to the Political Forum, and respect the sanctity of the Reloading forum.

But it was my observation that this thread has a topic associated with bullet seating depths and the effects on loads. That is what I will discuss here.

quote:

Originally posted by woods:
There is an small explanation of seating depth and how it affects pressure about 2/3 of the way down on the Hornady website.

quote:

To illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.

In a "normal" load with the bullet seated to allow about one 32nd of an inch gap (A) between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period (B), and the velocity obtained - 3500 fps - is "normal" for this load in this rifle.

Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start (C). Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps (D).

Essentially they are saying that seating a bullet deeper will decrease pressure. I do think that at some point the pressure will rise back up.

This does reveal a contradiction in almost every reloading manual that I have read. When they are talking about seating depth, most agree that seating the bullet deeper into the neck (creating longer freebore) reduces pressure.

But, when you read the section on bullet crimping, the reasoning is; cartidges in a magazine experience recoil; recoil can cause bullets to be pushed farther into the case, thus causing unsafe rise in pressure when fired.

Now, if they are specifically referring to this occuring with straight walled cases, they all fail to make that distinction. If they are saying that this can occur with any cartridge, then there must be a point when seating the bullet deaper can cause an increase in pressure.

quote:

Originally posted by steve4102:
I have a question about bullet set back, reduced case capacity and pressures in a bottle neck rifle cartridge.

Lets say that I worked up a load with 25.2gr of Ramshot TAC, a 55gr Sierra SPT at 2.260in OAL for a 223 AR-15. Ramshot lists this load at 49,000psi.

What would happen to the pressures in a load like this if the bullet were to become severely set back during the cycling of the action? I guess what I am asking, is there enough pressure increase from bullet set back to have a catastrophic failure in a bottle neck cartridge?

Quickload input:
a) Sierra 1360 SPT 55 gr. bullet is .710" long
b) 20" barrel
c) 25.2gr of Ramshot TAC
d) 2.26" OAL
e) 3626 psi start pressure[ 2.26" max that will fit in AR magazine, but will not reach the lands in any AR-15s I have. If we jam into the lands, we would raise start pressure to 5,000 psi]

Quickload outputs:
a) 47,653 psi
b) 3,018 fps
c) powder-case fill ratio 95.6%
---------------------------------------------------------
If we shove the bullet as far back as we can and still have some neck- bullet contact:

Quickload input:
a) Sierra 1360 SPT 55 gr. bullet is .710" long
b) 20" barrel
c) 25.2gr of Ramshot TAC
d) 1.9" OAL
e) 3626 psi start pressure

Quickload outputs:
a) 66,834 psi
b) 3,259 fps
c) powder-case fill ratio 110.4%
---------------------------------------------------------
What does it all mean?
a) If you push the bullet all the way into the case, you still can't get up to my 223 working pressure of 72,000 psi.
b) TAC is a ball powder, which have a high bulk modulus [difficult to compress] and so I doubt you can get 110.4% fill ratio without squishing the bullet with the seater die.

What does all THAT mean?
No, your bullet won't go back, and if it did, still no problem.

To give you some perspective, Malasian 5.56 Nato ammo with 55 gr FMJ will do 3,300 fps from an AR-15. It is loaded hot.

... and Max SAAMI pressure for 223 Rem is 55,000psi.

And you say that 66,834 psi is under a "working pressure" of 72,000 psi.

Thanks, but no thanks.

I mean, that the data you posted is revealing and meaningful for this discussion.

Personally, I would prefer to stay under the SAAMI specs to be safe.

Would someone please find and post a link to some possibly authoritative source that postulates the theory that seating deeper increases pressure. I did a search and came up with the Hornady source, any of you that say that seating deeper while keeping the combustion chamber the same size increases pressure, then let's see it.

I ran your load throught Load From A Disk and it said it was a 85% load denity at 57K psi. If the bullet was seated to 2.145"oal (on the powder a 100% desity) the pressure would be 67K psi.

Evidently Quick Load or Load from a Disk programs do not take into account the freebore of the rifle. In the original question posted by Steve the combustion chamber dimensions did not change only the seating depth of the bullet.

I will certainly concede that if you keep the distance to the lands the same distance along with the deeper seating of the bullet then the pressure would increase.

quote:

Originally posted by woods:
Would someone please find and post a link to some possibly authoritative source that postulates the theory that seating deeper increases pressure. I did a search and came up with the Hornady source, any of you that say that seating deeper while keeping the combustion chamber the same size increases pressure, then let's see it.

I can`t find a link to a web site, but the VithiVouri (sp?) manuals have a piece on deep seating in small straight walled cartridges and claim very large % of pressure increases. They use a 9mm as an example and show about a 6K psi piezo increase in pressure with a 2mm change in seating. The cartridge runs at 35K piezo max CIP so 6K psi is about a 15% jump in pressure or could make a max load a "proof load".

Bottle neck cartridges have the major percentage of their volume in the larger "body" of the case. The bullet diameter is quite a bit smaller then the body diameter and takes up less space. I doubt you will find much difference in pressure with seating changes in them.

Here is an article I found online. Note second-to-last paragraph.

quote:

Originally posted by woods:
Evidently Quick Load or Load from a Disk programs do not take into account the freebore of the rifle. In the original question posted by Steve the combustion chamber dimensions did not change only the seating depth of the bullet.

I will certainly concede that if you keep the distance to the lands the same distance along with the deeper seating of the bullet then the pressure would increase.

Quickload does not know where the lands are, but it does know how much volume is in the case when bullet is seated deeper.
To compensate for jamming into the lands, one must manually change the start pressure from 3,000 psi to 5,000 psi to get the velocities and pressure to match results.

quote:

Originally posted by mike_elmer:
Here is an article I found online. Note second-to-last paragraph.

Okay, that's a start

quote:

Always start well below the maximum charge listed and look for pressure indications. Seating the bullet too close to the lands will result in an increase in pressure, and seating a bullet too deep in a very small capacity case like the .300 Whisper will also result in a pressure increase. Use caution when developing loads in high performance handguns.

So he says that seating a bullet too deep in a very small capacity case will result in a pressure increase. Perhaps. I don't know Mr. Brown and don't doubt him but that is not the general situation we were talking about. Some here posted an immediate "yes" to the question Steve posted about his 223 cases. I particularly would like to see what those posters have to offer because in the situation Steve was describing I would think that the pressure would decrease. Seem to be supported by Hornady but would like to see evidence otherwise.

In my tests I know that velocity decreases when I seat the bullet significantly deeper (.2 or more off the lands), usually to fit a mag. One reason for decreases in velocity is a decrease in pressure. When loaded single shot just off the lands the velocity has increased significantly.

Bullet pinched by neck & neck pinched by chamber....big effect on pressure.
Bullet jammed in lands..........................................medium effect on pressure
Bullet pushed back into case................................ small effect on pressure.
Bullet bigger than grooves.....................................no effect on pressure

It has been suggested that the bullet starts to encroach on case volume once it passes the shoulder neck junction. Not so. It encroaches on case volume regardless of where it is. However, if the bullet is pushed too far back into the case that is, beyond the neck, it could lie skew and block the case mouth when fired! This won't happen if the case has a compressed charge or is full. Something to be remembered when considering straight walled pistol cartridges - they are loaded with double based, fast burning pistol powders. These cannot be expected to behave in the same way as slow burning, single based rifle powders.

Based upon information printed in Hornady, and Lyman manuals regarding the reasons for crimping bullets, I would conclude that "Yes", you could experience an increase in pressure if the bullet is seated too deep into the cartridge.

Straight wall cases are probably more suseptable to high pressure from seating too deep, but I would not assume that shouldered cases wouldn't experience a dangerous spike, too.

quote:

Originally posted by mike_elmer:


Straight wall cases are probably more suseptable to high pressure from seating too deep..

Do you think so?
When did you first suspect?

quote:

Originally posted by tnekkcc:

quote:

Originally posted by mike_elmer:


Straight wall cases are probably more suseptable to high pressure from seating too deep..

Do you think so?
When did you first suspect?

You're a good one to talk... you can't even stay within specs!!

quote:

Originally posted by mike_elmer:
Based upon information printed in Hornady, and Lyman manuals regarding the reasons for crimping bullets, I would conclude that "Yes", you could experience an increase in pressure if the bullet is seated too deep into the cartridge.

Based upon information printed in Hornady, and the lack of posted information posted here from the Lyman manual regarding the reasons for crimping bullets, I would conclude that "No" you can not experience an increase in pressure if the bullet is seated too deep in the cartridge, unless the bullet is seated past the neck into the case body area or the case is a very small capacity cartridge.

quote:

...and the lack of posted information posted here from the Lyman manual...

I do not know which edition you have, but in the 48th Edition, it IS IN THERE. I would also contend that a 45-70 is not a low capacity case. Yet, I would bet that you can raise pressure if you seat the bullet too deep.

quote:

Originally posted by mike_elmer:

quote:

...and the lack of posted information posted here from the Lyman manual...

I do not know which edition you have, but in the 48th Edition, it IS IN THERE. I would also contend that a 45-70 is not a low capacity case. Yet, I would bet that you can raise pressure if you seat the bullet too deep.

Well, what does it say?????

Please post or synosize the data or verbage you are alluding to and we can discuss it!!!!

Thanks guys, I appreciate your input.

Here is a test done by Barnes on how seating depths affects accuracy, pressure and velocity. Scroll down to "From the Lab".
http://www.barnesbullets.com/r...007-barnes-bullet-n/

I guess my main point in posting this question was to find out if there is enough increase in pressure to destroy a rifle due to bullet set back. It's clear that pressures can and do change with seating depth, but can this change (deeper) be enough for a catastrophic failure?

Hey steve, I forgot about this and glad you found it. Here is the chart


Brief explanation;

• the blue bars are ball powders,
  
• the red bars are extruded,
  
• the first set of bars above the caliber are at .025" off,
  
• every set of bars goint to the right in that caliber is additional .025" off,
  
• except 300 wtby where they couldn't get close to the lands

The 308 with ball powders shows decreased pressure with increased seating depth

The 308 with extruded powders shows a general decrease in pressure until seated .125" off lands

The 30-06 with ball powders shows a drastic decrease in pressure between .050" and .075" and then a slight increase

The 30-06 with extruded powder show a steady decrease in pressure with increased seating depth

The 300 WSM with ball powder shows a general decrease in pressure with increased seating depth

The 300 WSM with extruded powder shows a decrease until .075" off and then goes back up

The 300 win mag with ball powder shows a steady decrease in pressure with increased seating depth

The 300 win mag with extruded powder shows an increase between .025" to .050" and then a general pressure decrease with increased seating depth

The 300 Wtby shows a steady decrease in pressure with increased seating depth with both ball and extruded powders

The 300 RUM with ball powders shows a steady decrease in pressure with increased seating depth

The 300 RUM with extruded powders shows an up and down but generally steady pressure

My point is that in several of these instances the pressure is reduced with increased seating depth and that seems to be a general trend shown on this chart. IMO this supports the Hornady info in that if you increase the seating depth, generally speaking, you can expect lower pressure.