Understanding Pressure

[savagedasher]

Before you start thinking you know the gospel on the relationships of pressure, chamber finish (surface texture) and brass you should take a look at Varmit Al's pages. In particular check out the following topics.
1. 243 Model 7 FEA (FEA = finite element analysis)
2. Rifle action stress
3. Rifle chamber finish
4. Friction Test results
If you are not a mechanical engineer a lot of the language may be new to you. However his methods of analysis are common place in mechanical design today and are used in every company that does any sort of critical mechanical design.
I have argued these topics many times with people who insist that it is important for the case to grip the chamber.
It is unreasonable to expect your brass to be a mechanical brake in order to protect your action.
Your action should be capable of handling the firing loads without regard to the brass gripping the chamber simply because solvents or rain may get into a rifle chamber. Your rifle should not be damaged due to a small amount of liquid in a chamber or on a case.
If you use your brass for a brake you will on the path to case separations.
A very small amount of water or lubricant (flim) will not hurt a thing. In fact the Japanese, Dutch, the US and other countries have used oiled, waxed and greased cartridges to aid extraction in automatic weapons. HK and others even flute their chambers to insure cases are easy to extract.
If your bench rest action cannot handle a slight film of solvent left in the chamber by accident you probably should find a more rugged action.
Yes, If your chamber, bore and ammo are drowned in liquid you might cause a bore obstruction that damages something but I am not advocating that.
Anyway he covers analysis of a Rem 7 action and the effect of surface texture of a rifle chambers at several several values.

Then your saying the article is wrong . Larry

 

[Webster]

Savagedasher; thank you, when I apply the brakes on anything I drive I want 100% contact between the friction surfaces, when I apply my brakes I do not want to get into an emergency situation unless I have 100% contact between the road and tire..


I do not want to trap air, lube, water or oil in the hash mark finish, by design the hash marks will trap the air, lube, water and oil. If the surface has a glass finish there is not place to trap anything.


Again, I do not want anything between the chamber and case but air, I do not want a lot of air and then it goes to fluids and things that flow. Air is a fluid because it flows, air is a compressible; when I pull the trigger air gets out of the way and if is does not is can be compressed. Oil and water are also fluids, both flow but it is not possible to compress water, it is not possible to compress oil, if my chamber has cross hatches oil and water will act like ball bearings; and that is something I try to avoid I am the fan of cutting down on all that travel.


"Again", I do not want anything between the chamber and case but air"; I want the air I have between the case and chamber to be clean air, I do not want dirt, grit and or grime between the case and chamber because when the air leaves the dirt, grit and grime leaves with it. Dirt, girt and grime can not flow as fast as air.

F. Guffey

It's all non-sense that you make up.

 

[savagedasher]

It's all non-sense that you make up.

Like I said I give you win.
But it's not a matter of want .
There is a reason for the finish in a chamber. Regardless of your want . Larry

 

[fguffey]

When I pull the trigger I want the case to lock onto the chamber, for me there is nothing that locks together like 100% contact. In my opinion cross hatching is a bad habit.

I know, there are glaze breakers, I always ask what it is that is bad about the glaze. I am told those parts have to run together until they fit and I ask; after they fit what is left, a glaze?

F. Guffey

 

[Webster]

When I pull the trigger I want the case to lock onto the chamber, for me there is nothing that locks together like 100% contact. In my opinion cross hatching is a bad habit.

I know, there are glaze breakers, I always ask what it is that is bad about the glaze. I am told those parts have to run together until they fit and I ask; after they fit what is left, a glaze?

F. Guffey

The more texture you have the more resistance to movement between two surfaces. Smother surfaces less friction. You have it backwards. Smooth surfaces do not lock together.

 

[JRS]

From a well known and highly regarded builder of competition rifles:

"All chambers are polished and free of tool marks, thus minimizing friction between both the brass and chamber, and more importantly, the bullet and lead angle".

 

[fguffey]

The more texture you have the more resistance to movement between two surfaces.

Now we are back to talking about that area where the tire meets the road; I mean you said two surfaces. From the beginning I assumed we were talking about 360 degrees, square inches and 100% contact and then it must have gotten complicated because I thought we were talking about 'in all directions'.

When my case locks onto the wall of the chamber it is not moving, I know, I have heard all types of claims about the shoulder moving and the case head moving etc. I am the fan of cutting down on all of that travel and I am the fan of 100% contact in all directions.

F. Guffey

 

[rogn]

Just going back to the brakes for a chuckle- the highest performance disc brakes use crosshatched and cross ventilated rotors. So contact is< 100%. Crosshatching engine cylinders when new rings are involved allows wear in and matching of surfaces. Glazed surfaces indicate worn out. 100%

 

[spclark]

Ever take a look at dry-track racecar tires? They're usually slick, no tread.

Wet track is different, they have sipes or grooves for water to go to so it's not caught between track & tire surface.

Mirror-polished chambers I'd avoid. Better to have fine texture - very fine indeed - to allow brass to 'conform' during peak pressure interval, relieve forces directed backwards AND forwards.

 

[Zero333]

OK folks...

I'm gonna stir this pressure pot a little, concerting chamber finish and pressure...

Watch this video from the 12:00 minute mark to the end (16:00), you might learn a thing or two, instead of assuming.

Don't just watch one minute of it, cause it's the last 2 minutes that explains everything. And don't correlate this to benchrest shooting because BR loads rarely reach max pressures, let alone over pressure.

 

[fguffey]

Mirror-polished chambers I'd avoid. Better to have fine texture - very fine indeed - to allow brass to 'conform' during peak pressure interval, relieve forces directed backwards AND forwards.

There is an outside chance I am the only one with a gage that could have measure 'the texture' I had an electronic Pratt and Whitney gage that measured down to .000005" and that made it useless. I removed the electronics and added a dial indicator; and now it is one smooth running height gage. I have fired cases in chambers with .127" clearance without the case moving, and it boggles the mind when I say the shoulder did not move. I have tested receivers with loads that have destroyed the case, all of the damage to the case happened on the end of the case that was not supported. Never have I had a case to skid nor have I ever removed a case that mirrored a cross hatch pattern. I have never removed a case from a chamber with brass filings caused by a rough chamber.

Again, all I want between my case and chamber is air, I do not want a lot of air and the air I do have should be clean because dirty air will dull the finish of my chambers. There is an advantage to brass, brass is embeddable, there is a problem with that. When something abrasive is embedded into the case there is a chance the surface inside of my sizing dies will dull.

F. Guffey

 

[Webster]

There is an outside chance I am the only one with a gage that could have measure 'the texture' I had an electronic Pratt and Whitney gage that measured down to .000005" and that made it useless. I removed the electronics and added a dial indicator; and now it is one smooth running height gage. I have fired cases in chambers with .127" clearance without the case moving, and it boggles the mind when I say the shoulder did not move. I have tested receivers with loads that have destroyed the case, all of the damage to the case happened on the end of the case that was not supported. Never have I had a case to skid nor have I ever removed a case that mirrored a cross hatch pattern. I have never removed a case from a chamber with brass filings caused by a rough chamber.


If the case doesn't have lube on it 50,000 PSI will expand the case against the chamber regardless of the surface finish as long as there isn't a head space problem.

All you talk about is gauges and measurements. Why don't you tell us about how you perform at the range. By the way I operated a $50,000 Optical Profilometer at work.

 

[JRS]

 

[XBBR Shooter]

Chamber finish is always a hotly debated subject, and the people that believe in scored chambers will never give up...
... but here are some things to think about.

The Blish effect (google it) does NOT depend on the surface finish - it is working at the molecular lever. Polished brass will stick to steel, under pressure, just as well as brass with a "cross hatch" finish.

And, if you think that the thin walls of a soft brass case (that you can crush with a 99¢ pair of pliers), can protect two heavy, ballistic steel lugs, I have a bridge to sell you.

Think about it - we worry about FL sizing too much, and pushing the shoulder back too mush, because it causes head separations. So, if the body is sticking to the chamber walls, why is the case head "going south" and crashing into the bolt face.. if it is strong enough to protect our helpless bolt lugs?



The brass walls cannot protect anything -- and the steel lugs are so damn hard, that they are almost indestructible...

Exhibit - A...

A Remington 700 bolt from a 22-250 that was erroneously loaded with ball pistol powder ("Well, Golly, it looked like H-414"). Pressure was estimated to be 270,000+ PSI.

The case head re-formed into the space in the bolt face (AFTER the extractor and sides were blown off)

... now here is the best part.

The bolt and action were fine, as far as head space was concerned - the lugs were not damaged, and there were no marks or setback in the receiver shelf. If you were willing to push fired cases out with a cleaning rod, you could have cleaned it up and used the bolt as it was.

But, desiring real extraction a new bolt was bought, and the gun is in service today.

Now, if you want to make some silly argument that the brass case is "protecting" the fragile bolt... you need to think about.

Second.

Most of us know that the proper way to set up your sizing die (FL or Bump) is to set it so the stripped bolt (no pin or ejector) will not close all the way by it's own weight on a properly sized case.

The reason for this is that as the bolt closes, the bolt face moves slightly forward - and when the bolt handle drops half way down, it is because the case has been pushed forward and the shoulder is against the chamber shoulder, and the case head is being pushed by the bolt face - in other words... the case is 1 or more thou LONGER than the chamber.
This is called "Crush".

So, when you fire this $5,000 benchrest rifle, the case is ALREADY hard against the bolt face, so ALL of the pressure is transferred to the bolt lugs.

Why isn't that rifle falling apart, if the "theory" of cases protecting bolts is true?

Because that theory is pure...

 

[dcali]

The Blish effect (google it) does NOT depend on the surface finish - it is working at the molecular lever. Polished brass will stick to steel, under pressure, just as well as brass with a "cross hatch" finish.

I was under the impression that the Blish effect was discredited, and does not, in fact, exist? That said, all this talk about water in the chamber, friction, etc - it's a small effect worth mentioning. It's not going to shear your lugs, but it can, from what little testing I have seen, have a small impact on pressure - akin to firing fully resized brass vs neck sized. Small, but measurable.

 

[fguffey]

Polished brass will stick to steel, under pressure, just as well as brass with a "cross hatch" finish.

I am the fan of the case locking onto the chamber, I am also the only fan of the smooth/shiny finish. I can put a cross hatch finish on just about anything but I have never tried to put a cross hatch finish on a chamber with a taper.

F. Guffey

 

[XBBR Shooter]

I was under the impression that the Blish effect was discredited, and does not, in fact, exist? That said, all this talk about water in the chamber, friction, etc - it's a small effect worth mentioning. It's not going to shear your lugs, but it can, from what little testing I have seen, have a small impact on pressure - akin to firing fully resized brass vs neck sized. Small, but measurable.

The Blish effect has not been discredited and does exist.

What "little testing" have you seen? And how relevent is it? Can you measure the difference between FL and neck sized cases? Where have you seen this? Any difference would below the noise level.

 

[fguffey]

Can you measure the difference between FL and neck sized cases?

Measuring is one thing; understanding the difference is another thing. I have neck sizing dies; I do not use them but I have them JIC. And then there is a difference between returning a case to minimum length and sizing a case for a chamber with a know length.

F. Guffey

 

[M-61]

Measuring is one thing; understanding the difference is another thing. I have neck sizing dies; I do not use them but I have them JIC. And then there is a difference between returning a case to minimum length and sizing a case for a chamber with a know length.

F. Guffey

What do you mean by "I have neck sizing dies; I do not use them but I have them JIC."? In case of what?

 

[dcali]

The Blish effect has not been discredited and does exist.

What "little testing" have you seen? And how relevent is it? Can you measure the difference between FL and neck sized cases? Where have you seen this? Any difference would below the noise level.

I believe someone posted some pressure measurements here or elsewhere and you could in fact see a small difference (higher pressure with neck sized brass), due presumably to the energy required to expand the case. I can't recall where I saw the chamber friction work. Maybe precision shooting a long time ago?

As for Blish - all I know is that it is not taught in engineering schools, and I've never seen it discussed outside of the Thompson machine gun. If what he really meant was "friction", then yeah. But that's marketing, not engineering.