Lug setback? What am I missing?

[sedancowboy]

Are we all in agreement that:
same volume of chamber with the same psi, regardless of bolt face diameter transfers the same amount of energy onto the bolt lugs?

We are not!! Do you just disregard the math and science that has been presented here.
Prove to me using math formulas that your theory is sound? I gave you my formula and showed you my calculations as to why your theory is not valid. The math simply proves your theory false.
But your denying that a larger bolt face exerts more force than a smaller one does not make it so. There has been many people attempt to educate you and share their knowledge with you to no avail.
Reminds me of and old saying "I am only responsible for what I say not what you perceive".
I am sorry that my skills with the English Language has failed you.
So are you also saying that a hydraulic cylinder given the same pressure regardless of size does the same amount of work. I truly believe you know better.
Henry

 

[adam32]

Hydraulic cylinders don't shoot bullets with controlled explosions nor have equal and opposite reactions to anything.

You guys honestly believe that if you took a .223 and attached a Lapua case head onto it and ran a 55gr bullet with what 25grs of powder, that it'll produce the exact same force on the bolt lugs and rest of the action as a Lapua shooting a 300gr bullet?

That simply changing the diameter of the bolt face will instantly make a cartridge go from safe for many thousands of rounds to unsafe and might blow up?

 

[Tommo64]

Force=pressure X area, so it stands to reason that a larger bolt face, having a greater surface area, will exert proportionately more force on the lugs.

 

[birdiemc]

The pressure inside the chamber acting on the surface area of the bolt face, using the formula f=pa, is converted to pounds of force applied to the bolt face. Because the lugs aren't in contact with the pressure inside the chamber they are not directly affected by this pressure, but indirectly affected by the force acting on the bolt face transferred through the bolt. And the force acting on the bolt face is dependent on the size of the surface area.
Think of a ship's sail (big area) in a 40 mph wind vs. a notecard (small area) in a 40mph wind. To pressure acting on the 2 is equal but you can hold a notecard in your hand, but the sail would send you flying through the air. So the force is obviously greater with the bigger surface area.

The example of a bulldozer track was mentioned at one point. That is an example of the force (weight of machine) being evenly distributed (divided) over a greater surface area thereby reducing the pressure to the ground...same formula though just rearranged p=f/a

 

[birdiemc]

Hydraulic cylinders don't shoot bullets with controlled explosions nor have equal and opposite reactions to anything.

You guys honestly believe that if you took a .223 and attached a Lapua case head onto it and ran a 55gr bullet with what 25grs of powder, that it'll produce the exact same force on the bolt lugs and rest of the action as a Lapua shooting a 300gr bullet?

That simply changing the diameter of the bolt face will instantly make a cartridge go from safe for many thousands of rounds to unsafe and might blow up?

Before this discussion I never would have believed it, but if only considering the pressure and surface area of the bolt face, then I'd have to say yes that seems to be the case

 

[adam32]

Before this discussion I never would have believed it, but if only considering the pressure and surface area of the bolt face, then I'd have to say yes that seems to be the case

In theory.

But I guarantee nobody would agree if I said that if you took a Lapua and rebated the rim to a standard mag that it would then be safe to run it over pressure (since the brass can handle it) and you would never have to worry about bolt lug setback...if that were true then EVERYTHING would have rebated rims.

 

[MNbogboy]

Hydraulic cylinders don't shoot bullets with controlled explosions nor have equal and opposite reactions to anything.

You guys honestly believe that if you took a .223 and attached a Lapua case head onto it and ran a 55gr bullet with what 25grs of powder, that it'll produce the exact same force on the bolt lugs and rest of the action as a Lapua shooting a 300gr bullet?

That simply changing the diameter of the bolt face will instantly make a cartridge go from safe for many thousands of rounds to unsafe and might blow up?

Not just the case head the case body diameter determines what forces that pressure will make. Actually someone mentioned it earlier the actual internal diameter.
A lapua case necked down to 224 pushing a 55 grain bullet at 60000 psi (? Maybe 3800 fps) would produce the same lug force as a 338 300 grain at 60000 psi (? 3000 fps ??).

The 300 would kick like a mule and the 224 would be sweet.

Now what you are saying is correct the size of the case head itself doesn't matter a 223 with a case head the size of the lapua would have would have far less force against the lugs because the case body diameter is so small.

Good post, think it gives all a better perspective on why rifle designs are what they are.

 

[Mram10us]

We are not!! Do you just disregard the math and science that has been presented here.
Prove to me using math formulas that your theory is sound? I gave you my formula and showed you my calculations as to why your theory is not valid. The math simply proves your theory false.
But your denying that a larger bolt face exerts more force than a smaller one does not make it so. There has been many people attempt to educate you and share their knowledge with you to no avail.
Reminds me of and old saying "I am only responsible for what I say not what you perceive".
I am sorry that my skills with the English Language has failed you.
So are you also saying that a hydraulic cylinder given the same pressure regardless of size does the same amount of work. I truly believe you know better.
Henry

A simple "no" would suffice Funny how I ask an honest question and you get so spun up. Maybe you could relax a bit

 

[birdiemc]

In theory.

But I guarantee nobody would agree if I said that if you took a Lapua and rebated the rim to a standard mag that it would then be safe to run it over pressure (since the brass can handle it) and you would never have to worry about bolt lug setback...if that were true then EVERYTHING would have rebated rims.

I googled rebated rim cuz I dont know what that is . Looks to me like the rim is turned down to a smaller OD, am I understanding this correctly?
If so, then I would say using the formula we've been discussing and considering ONLY chamber pressure and bolt face diameter, the math works out that the force applied to the bolt would go down proportionally to the reduction in bolt face diameter.
I'm a nerd and love math so all I'm saying is that with this formula and 3 variables the numbers work. I am by no means saying I know squat about what's going on inside that chamber and how the case reacts with the chamber walls and all the stuff that has been thrown into this discussion...I'm not gonna fire up the lathe and turn down a case to try it because I dont even know what I dont know, just saying the math works "in a vacuum" as they say

 

[Mram10us]

The question was asked about getting the 230gr at 3000fps fired from both.
1. would the chamber pressure need to be equal?
2. would the lugs receive less force from the bolt?

 

[birdiemc]

Not just the case head the case body diameter determines what forces that pressure will make. Actually someone mentioned it earlier the actual internal diameter.
A lapua case necked down to 224 pushing a 55 grain bullet at 60000 psi (? Maybe 3800 fps) would produce the same lug force as a 338 300 grain at 60000 psi (? 3000 fps ??).

The 300 would kick like a mule and the 224 would be sweet.

Now what you are saying is correct the size of the case head itself doesn't matter a 223 with a case head the size of the lapua would have would have far less force against the lugs because the case body diameter is so small.

Good post, think it gives all a better perspective on why rifle designs are what they are.

Question for ya,
Internal pressure was mentioned a few times so far, which would be 60000psi pushing against the base then to bolt face...would the pressure acting onto the shoulder offset the force a bit in the other direction and cancel out some of the force transferred to the bolt face?
Where is the bullet physically located at peak pressure? In the neck still or out side?

 

[adam32]

Question for ya,
Internal pressure was mentioned a few times so far, which would be 60000psi pushing against the base then to bolt face...would the pressure acting onto the shoulder offset the force a bit in the other direction and cancel out some of the force transferred to the bolt face?
Where is the bullet physically located at peak pressure? In the neck still or out side?

Also the volume of said pressure plays a key role...

 

[Mram10us]

Would this be a good example?
280ai with .473" boltface v 7saum with .532" boltface. Almost identical powder to FPS comparison.
1. Is chamber pressure different?
2. Do the bolt lugs feel different amounts of pressure?

 

[birdiemc]

Would this be a good example?
280ai with .473" boltface v 7saum with .532" boltface. Almost identical powder to FPS comparison.
1. Is chamber pressure different?
2. Do the bolt lugs feel different amounts of pressure?

1. As volume increases, pressure decreases
So if the volumes are the same, and the charge weights are the same (same potential energy) then it seems the pressure should be the same inside the chamber
2. The 473 bolt face would transfer less force to the bolt, which would then be distributed over the surface area of the lugs resulting in lower pressure on the lugs, assuming the lugs have equal surface area on both bolts.