Lug setback? What am I missing?

[adam32]

I hope that is a typo because the pressure per sq in is the same over the larger area of the LM case head thus having more thrust on the lugs. If it is the same pressure it can't reduce it. It can add more force to the Lugs because of the larger surface area.

Really we are talking about lugs and abutments. The bottom lug abutment is the weak link in a Remington 700 action therefore as Kirby stated it was set back the most. Thus the 700 Action did not have the necessary safety margin to satisfy him when the LM was used...running above maximum pressures.

Fixed it for ya...

 

[adam32]

It's funny that people only bring up the Lapua...nobody seems to have a problem with the Norma case or the Wby...could it be since the Lapua brass is stronger therefore running excessively high pressures before seeing the normal pressure signs?

 

[Johnny Jr.]

I always assumed the forces on the boltface (and lug surfaces) was the ft lbs of energy derived from the bullet weight and it's speed out the barrel. I also presume expansion of the case and it's grip on the chamber wall would soak up some (maybe a lot?) of the energy reaching the bolt face (and lugs).
I know a 460 Weatherby action can handle 8000 ft lbs of energy and a Remington 700 338 LM can take 5200 ft lbs (Hornady.com). Does anyone know the max limit of the 700 assuming established safe loads? I'm thinking a 460 WM in a 700 is not a smart move.
If bolt face diameter and PSI determine the forces on the lugs and receiver then either cartridge should be fine

 

[J E Custom]

Everything isn't the same though, the only constant is X amount of chamber PSI. Literally everything else is different. That's why I asked if you shot a 55gr bullet out of a Lapua at the same X chamber PSI will it have the same force applied to the bolt lugs as a Lapua shooting a 300gr bullet at the same chamber PSI?

Or better yet, no bullet at all?

Sorry, it wouldn't.
Without a bullet you would get very little pressure, but the thrust on the bolt would be different if you shot another cartridge with a smaller or larger case head with no bullet, except it would not have enough thrust to damage/set the lug back.

Try this, If you had a piston that had 1 square inch of surface and you applied 1 PSI pressure, you would get 1 pound of force. If you increased the piston to 1 &1/2 square Inches and you applied 1 PSI to the larger piston it would produce 1 & 1/2 pounds of force on the piston. (PSI).

J E CUSTOM

 

[J E Custom]

It's funny that people only bring up the Lapua...nobody seems to have a problem with the Norma case or the Wby...could it be since the Lapua brass is stronger therefore running excessively high pressures before seeing the normal pressure signs?

The Weatherby is only a few thousandths smaller that the Lapua But the difference is there, only not as much as going from a standard bolt face. There are other cartridges that are lower pressures but have even larger case heads and can produce as much force as the smaller case head with more pressure.

Brass quality has nothing to do with lug set back, it is the size and pressure of the case head that effect the lug loading.

J E CUSTOM.

 

[adam32]

Brass quality has nothing to do with lug set back, it is the size and pressure of the case head that effect the lug loading.

J E CUSTOM.

So you've seen lug set back with a Lapua running at normal pressure? Because I only know of it happening when people run it overpressure since the brass quality masks the normal pressure signs...

 

[adam32]

Sorry, it wouldn't.
Without a bullet you would get very little pressure, but the thrust on the bolt would be different if you shot another cartridge with a smaller or larger case head with no bullet, except it would not have enough thrust to damage/set the lug back.

J E CUSTOM

There's ways to create pressure without a bullet.

But what about the 55gr bullet vs the 300gr? You're saying it'll be exactly equal force on the bolt lugs? So it should create the same exact recoil too then, right?

 

[birdiemc]

Roger.

Example:
we have 2 identical actions shooting the identical load, except the boltfaces. Wont the lugs and lug abatements see the same amount of pressure? Case and chamber walls account for very little (need another thread for that topic)

Let's see how this stands up in this thread...
If we make the assumption that the 2 cartidges create the same exact pressure, within the chamber, completely disregard all other variables... then what the majority of us are saying is no, the force transferred from the bolt face to the bolt to the lugs would not be equal in both. That's where all the math we did comes in to play. As well as the hydraulic jack discussion and the difference between a 1000lb weight on the table vs. 1000 lbs/ square inch on the table.

And as for all the rest of the discussion, that does not apply at all to what I just said cuz my experiment exists in never never land where other variables don't exist that would mess with my fairy tale setup

 

[Labwhisper]

It's funny that people only bring up the Lapua...nobody seems to have a problem with the Norma case or the Wby...could it be since the Lapua brass is stronger therefore running excessively high pressures before seeing the normal pressure signs?

I think that's where I came in.

 

[Mram10us]

If Kirby says he believes it, I don't necessarily have to fully understand it to accept it. Kinda like brain surgery. In this case he is 100% correct.

It doesn't matter to me who says it. We should never take advice without understanding the concepts involved. Just my thoughts

 

[Mram10us]

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?

 

[J E Custom]

So you've seen lug set back with a Lapua running at normal pressure? Because I only know of it happening when people run it overpressure since the brass quality masks the normal pressure signs...

I simply say that if a action is designed for a specific bolt load, and you exceed that It can set the bolt lugs back.

Recoil lugs and abutments are designed for the use intended. you wouldn't re chamber a 22 long rifle in 22 mag unless you had a death wish for the same reason, It wasn't designed for the extra pressure with almost the same bolt face diameter. The fact that Remington has adopted the 338 Lapua simply means that with standard loads it is safe. It doesn't mean that with heavy use or hi pressure loads that the 700 action will not get Lug set back over time.

Normally the bigger the cartridge, the bigger the bolt and bolt face. By designing bigger lugs and abutments this problem will normally not exist unless the design pressure and bolt load are exceeded.

J E CUSTOM

 

[MNbogboy]

There's ways to create pressure without a bullet.

But what about the 55gr bullet vs the 300gr? You're saying it'll be exactly equal force on the bolt lugs? So it should create the same exact recoil too then, right?

The force on the lugs always dependent on the chamber pressure and the size of the back of the chamber ( explained by JE Custom as piston size ).

Recoil is a different force dependant on the weight of the bullet and it's speed in a reaction to the weight of the rifle where thrust in each direction is equalized.
(For every force there is an equal and opposite reaction).

A 55 grain bullet at 60000 psi will create far less recoil than a 300 grain bullet at 60000 psi in the same rifle. Look at the muzzle energy of both.
But the forces on the lugs and abutments will be the same with both bullets at 60000 psi.

The larger the rear of the chamber diameter is the more static force is applied to the lugs & abutments. Because of the law Force = pressure x area.

The big diameter Lapua, Norma and Weatherby magnums require the stronger lugs & abutments because of their diameters.

Randy

 

[birdiemc]

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?

No...I'm trying to find a good video to show what we're talking about...the most promising one I found so far was an Indian guy that couldn't pick a language to speak...I think I heard 3 different languages in there