Does anyone know at what pressure sticky bolt lift occurs?

[RegionRat]

IMO, follow the guidelines of the manuals and don't forget that "pressure equals speed and speed equals pressure"

Yes, but.... I must remind folks that while experimenting with load development, you can find yourself in a situation where pressure can go to higher magnitudes while not generating a velocity that would alarm you.

Your basic concept is good advice. Load development that goes into unknown territory or when Wildcatting, is not for everybody.

 

[RegionRat]

Sticky bolts occur when the brass and chamber expand under pressure and when the pressure is removed the brass doesn't contract as much as the chamber due to differences in Young's modulus. The exact pressure depends on the barrel/receiver design but someone at LBL (Lawrence Berkley Labs if I remember correctly) estimated it to be around 70,000 PSI for a rifle cartridge.

There needs to be a little finer point put on the concept of multiple cycle issues versus single cycle issues.

Doom2 is correct in that when we look at the material strength of the brass, and a single high pressure cycle that exceeds the yield strength, we should expect trouble. However...

Depending on the initial hardness value of the case head material, it is still possible to see a difference in the events based on less pressure but more cycles. There is also the concept that the elastic modulus still allows some yield by definition. Without going all the way to yield pressure, but coming very close to it, we expect case heads and primer pockets to flow.

So just coming into that gray zone between the SAAMI or CIP specification and the yield pressure, can also give us a sticky bolt after just a few cycles. This is because buried in the concept of the yield strength, there is shear storage modulus and shear loss modulus that is time and cycle dependent, without even going all the way to the definition of yield. YMMV

 

[QuietTexan]

More means bigger cartridge,, better planning next time.
To me, it doesn't makes sense to cause high brass turnover -for more velocity -from a hunting cartridge.

Picking the correct cartridge is always best starting point. Hot rodding pipsqueaks because you can is fun to a point, but when work needs to be done the thumpers come out.

 

[Carey Farmer]

There needs to be a little finer point put on the concept of multiple cycle issues versus single cycle issues.

Doom2 is correct in that when we look at the material strength of the brass, and a single high pressure cycle that exceeds the yield strength, we should expect trouble. However...

Depending on the initial hardness value of the case head material, it is still possible to see a difference in the events based on less pressure but more cycles. There is also the concept that the elastic modulus still allows some yield by definition. Without going all the way to yield pressure, but coming very close to it, we expect case heads and primer pockets to flow.

So just coming into that gray zone between the SAAMI or CIP specification and the yield pressure, can also give us a sticky bolt after just a few cycles. This is because buried in the concept of the yield strength, there is shear storage modulus and shear loss modulus that is time and cycle dependent, without even going all the way to the definition of yield.

I full length size between every firing. So, no question my cases yield outward on every firing (after being yielded inward every resizing). As pressure expands the chamber, the brass yields further. If the steel chamber expands elastically over a range greater than the elastic range of the brass, then when the pressure is relieved the steel chamber puts the brass in compression.

Young's modulus for brass is only half that of steel, but barrel steels have yield strength that can be four or five times greater than brass. You see the problem - yield strain for brass is less than half the yield strain of barrel steel.

 

[243winxb]

If primer pockets become loose in 5 firing or less, pressure is to high.

 

[Mikecr]

If the steel chamber expands elastically over a range greater than the elastic range of the brass, then when the pressure is relieved the steel chamber puts the brass in compression.

It is possible to raise the operating function of a chamber.
An example setup for better extraction:
-Small diameter cartridge chosen
-Magnum diameter tenon
-Fine threading of the tenon
-Coned breech
-Tight clearances (very opposite of loose)
You might imagine doing this with a large shank Savage, custom coned bolt head, and chamber fitted for new 223Rem brass.
In this case you would have enough barrel steel and breech supporting the chamber to run higher than normal pressures without popping extraction (chamber interference fit).

Then there are other pressure problems with the brass, and these can be addressed as well.
Ackley improvement, and minimal sizing help.

Brass wants to go where it's been. This, due to realignment of it's grain structure.
IMO, the trick to keeping well challenged brass alive is to reduce or eliminate yielding, so brass stays right where it is.
And it takes a special plan up front -just for that.

A lot of folks would suggest that this is not worth it for more velocity. They're right.
There is more than just velocity though.
If you can run/find a good load into diminished returns, then diminished returns equals diminished variance of returns.
The prime example is the 6PPC at competitive pressures (75Kpsi+). Their pressure peak is flattened to a point that they don't even have to weigh charges. And the only reason their cases don't last is because they're not doing all the things I mention here.

 

[Carey Farmer]

It is possible to raise the operating function of a chamber.
An example setup for better extraction:
-Small diameter cartridge chosen
-Magnum diameter tenon
-Fine threading of the tenon
-Coned breech
-Tight clearances (very opposite of loose)
You might imagine doing this with a large shank Savage, custom coned bolt head, and chamber fitted for new 223Rem brass.
In this case you would have enough barrel steel and breech supporting the chamber to run higher than normal pressures without popping extraction (chamber interference fit).

Then there are other pressure problems with the brass, and these can be addressed as well.
Ackley improvement, and minimal sizing help.

Brass wants to go where it's been. This, due to realignment of it's grain structure.
IMO, the trick to keeping well challenged brass alive is to reduce or eliminate yielding, so brass stays right where it is.
And it takes a special plan up front -just for that.

A lot of folks would suggest that this is not worth it for more velocity. They're right.
There is more than just velocity though.
If you can run/find a good load into diminished returns, then diminished returns equals diminished variance of returns.
The prime example is the 6PPC at competitive pressures (75Kpsi+). Their pressure peak is flattened to a point that they don't even have to weigh charges. And they only reason their cases don't last is because they're not doing all the things I mention here.

Thank you Mikecr. Your clarity of thought is impressive.

 

[Rich Coyle]

If primer pockets become loose in 5 firing or less, pressure is to high.

Based on what?

 

[jessej]

If primer pockets become loose in 5 firing or less, pressure is to high.

"To high" is a relative term.
Blown primer on first firing May be someone's "to high"
Loose primer on 10th firing May be someone's "to high"


I am alive, straddling the edge between sublime, and ridiculousness, and this is exactly where I belong

 

[Doom2]

There needs to be a little finer point put on the concept of multiple cycle issues versus single cycle issues.

Doom2 is correct in that when we look at the material strength of the brass, and a single high pressure cycle that exceeds the yield strength, we should expect trouble. However...

Depending on the initial hardness value of the case head material, it is still possible to see a difference in the events based on less pressure but more cycles. There is also the concept that the elastic modulus still allows some yield by definition. Without going all the way to yield pressure, but coming very close to it, we expect case heads and primer pockets to flow.

So just coming into that gray zone between the SAAMI or CIP specification and the yield pressure, can also give us a sticky bolt after just a few cycles. This is because buried in the concept of the yield strength, there is shear storage modulus and shear loss modulus that is time and cycle dependent, without even going all the way to the definition of yield. YMMV

I want to clarify something. Brass, meaning the case wall itself along with the neck and shoulder, exceed the the yield stress on each firing, This is why the case does not return to its original size and we are left to resize. The function of the case on firing is to seal the chamber and to fulfill this function it must deform to fill the chamber. The actual pressure containment is performed by the barrel, receiver, bolt and lugs, along with with the case head.

 

[243winxb]

Based on what?

See post #30.

Plus-

Plastic deformation-This whole relationship centers around the elastic limit for the brass you are using and what the elastic limit is. the elastic limit is the point at which stresses can occur to an object and it will return to it's relative shape. Once you have reached the deformation stage it no longer returns to relative shape. this is a very simplified version of this topic as it pertains to engineering mechanics of materials.
This is meant to be a guide and to keep you within safe/acceptable limits for pressure for your purposes.


5 shots or less-
"Creep" is a progressive plastic deformation that increases with time, even when the stress is below
the yield stress of the material.


Past 76,000 PSI, brass is scrap.

 

[Rich Coyle]

@243winxb,

You used the term "within safe/acceptable limits". I think to some "acceptable" is what the lawyer says. "Safe" on the other hand is what wildcatters work within.

I once built a 7-.348 Win. One firing and it would not hold a primer. I never had smoke come out anywhere except the muzzle. I had it rechambered with a cartridge a few thousandths larger and was able to get at least ten firings using about the same load. Obviously both were "safe". One was not acceptable to me.

 

[RidgeTop]

I have heard 70% of recoil pressure is held by the purchase the case has on the chamber. The other 30% is left up to the bolt.
If you want to risk high pressure and sticky bolt you might be looking at 18,000, literally, if the bolt lets loose that is where it goes. If you want more power, get a bigger gun. JMO

 

[Rich Coyle]

I have heard 70% of recoil pressure is held by the purchase the case has on the chamber. The other 30% is left up to the bolt.
If you want to risk high pressure and sticky bolt you might be looking at 18,000, literally, if the bolt lets loose that is where it goes. If you want more power, get a bigger gun. JMO

What does one do if they already have one of the largest cases on the market?