How can the mechanical stress exerted by DG cartridges on the action be estimated? Peak pressure alone is not a solution

Accidental Villain · Mar 3, 2026

grand veneur said:
I own a custom rifle caliber 460 Weatherby Magnum built with a Brevex Mauser action, with which I have fired hundreds of rounds over the last 30 years. No sign of any wear.

Well,, no surprises there. The Brevex M400 action is made of superb quality chrome moly steel. Shoot it with the greatest confidence for 100 more yrs.

Choupique · Mar 3, 2026

roklok said:
read that case design has a large impact on bolt thrust. Less case taper= less bolt thrust, more taper= more bolt thrust.

This was my initial thought reading the OP. Always glad to find myself some confirmation information!

It seems .375 h&h could possibly generate more bolt thrust than say, 375 weatherby, due to case geometry.

It would also be incredibly difficult to approximate the friction between the case and chamber for simulation purposes. It starts out with nearly zero friction, and then increases to a very high value during the initial burn, and then relaxes over time slightly. Complex stuff going on in there! I think the only good way to find the true answer would be strain gauges on the action chamber and a load cell under the case head. I bet the stress exerted on the action varies tremendously shot to shot for a given rifle, much less a given caliber in different rifles. I wonder if manufacturers do something like that as part of the action proofing process these days? The instrumentation and computing power would not be terribly expensive these days but it may be an instance of figuring out more stuff than you really need to know.

Jefferry404 · Mar 3, 2026

FYI,
I design custom barrel contours for bolt rifles, mostly with integral quarter rib, sling band and front sight bases (my passion). Most use standard cartridges but some, like the 550 Magnum and 416 Cheytac, pushing the limits. As such, I have to ensure not getting too crazy on the contours and need calculate the barrel stress, chamber stress and bolt thrust using textbook math. And once upon a time, confirmed the math with 3D static simulation.
Here is an example the analysis for my custom contour:

and what a sim results looks like:

BlackRhino · Mar 5, 2026

@ Nhoro
I also would assume that engeneers design rifles with a sufficient safety margin. Unfortunately there have been several cases of Blaser R93 blow-ups causing severe injuries. Later the company changed
the design (Blaser R8). Why? Very, very probable because the R93 action was not strong enough.

Nhoro · Mar 5, 2026

BlackRhino said:
@ Nhoro
I also would assume that engeneers design rifles with a sufficient safety margin. Unfortunately there have been several cases of Blaser R93 blow-ups causing severe injuries. Later the company changed
the design (Blaser R8). Why? Very, very probable because the R93 action was not strong enough.

That's fighting talk !

Without knowing exact details it is hard to say- maybe wrong powder in handloads ? But I think the Blaser action has more moving parts and they are smaller and statistics are against them. Also one small malfunctioning part in lockup can cause a problem. I don't think that is what you are angling at, you are questioning why do people only discuss pressure.

Jefferry404, you have obviously done the sums and solidworks simulation. I have not seen a mauser or Remington bolt fail if it had proper metallurgy. The few blown up guns I have seen are a chamber split. So I would guess that is the weakest point. And surely all of the parameters are dependent or related to case pressure. So discussions centre around that parameter ?

Jefferry404 · Mar 5, 2026

Significant difference between failure (tensile strength) and safety margin (yield strength). My analysis are for safety margin as the proof test loads are usually 1.3-1.5x. In stress analysis, the safety factor of 1.0 means the stress psi is equal to the material yield strength and the materials (barrels and lugs) are elastic deformation.
Greater than 1.0, is plastic deformation. This means that some of the material at the inner radius stays deformed. I think of Tangential micro cracks. Next firing, more plastic expansion and cracks.
At this point to complicated for me and most (hence safety margin greater than 1.0)
Probably never know it is happening.
But, I need to compare contours, cartridges and pressure and this is how I do it.

Huvius · Mar 5, 2026

Choupique said:
This was my initial thought reading the OP. Always glad to find myself some confirmation information!

It seems .375 h&h could possibly generate more bolt thrust than say, 375 weatherby, due to case geometry.

It would also be incredibly difficult to approximate the friction between the case and chamber for simulation purposes. It starts out with nearly zero friction, and then increases to a very high value during the initial burn, and then relaxes over time slightly. Complex stuff going on in there! I think the only good way to find the true answer would be strain gauges on the action chamber and a load cell under the case head. I bet the stress exerted on the action varies tremendously shot to shot for a given rifle, much less a given caliber in different rifles. I wonder if manufacturers do something like that as part of the action proofing process these days? The instrumentation and computing power would not be terribly expensive these days but it may be an instance of figuring out more stuff than you really need to know.

As I understand it, the cartridge case has full intimate contact/grip at around 10K psi chamber pressure. If that is so, the bolt thrust should be minimal through the build to peak and descent back down. I think (if my memory serves) there are some instances of detonation in semi-auto firearms where the base of the cartridge is still in place which leads me to think that at extreme pressures the case can act as sort of an obstruction - although in the chamber rather than in the bore.

Choupique · Mar 5, 2026

Huvius said:
at extreme pressures the case can act as sort of an obstruction - although in the chamber rather than in the bore.

Absolutely, which would be difficult to quantify. You can readily observe this effect with hot handloads and stiff bolt lift, which is resulting from the case refusing to move aft in the chamber. How that grabby-ness changes through the course of the combustion event would be tough to accurately simulate without a lot of empirical data to refine the results. It is relatively simple to make some worst case assumptions, like peak pressure x case head area = thrust and have an overbuilt action, which I'm sure is what we usually get.

It could however be readily measured with a specially made test rifle. I'm sure the bigger manufacturers are doing that these days and guarding the information closely.

C.W. Richter · Mar 5, 2026

Less is best for the Manufacturer sales today, until...(Not all, but most!)

BlackRhino said:
@ Nhoro
I also would assume that engeneers design rifles with a sufficient safety margin. Unfortunately there have been several cases of Blaser R93 blow-ups causing severe injuries. Later the company changed
the design (Blaser R8). Why? Very, very probable because the R93 action was not strong enough.

Jefferry404 · Mar 5, 2026

I do not know but In my bolt thrust calculation, I try to model the sticky brass by using the coefficient of friction between dry brass and steel and the brass surface area, this then reduces the back pressure on the bolt.
Is it perfect, no, but for comparing designs, adequate. I believe in quantitative vs qualitative descriptions.

Mark A Ouellette · Mar 5, 2026

Jefferry404 said:
I do not know but In my bolt thrust calculation, I try to model the sticky brass by using the coefficient of friction between dry brass and steel and the brass surface area, this then reduces the back pressure on the bolt.
Is it perfect, no, but for comparing designs, adequate. I believe in quantitative vs qualitative descriptions.

I appreciate all the thought concerning brass friction in chamber reducing bolt thrust, but how big a factor could that be?

Could it be equal to 1,000 psi directed outward to the chamber rather than backward to the bolt?

Jefferry404 · Mar 5, 2026

I was suprised at the reduction. In the pass i used the QL bullet pressure as a way to model but then went to the friction form below:

PI()*AW24^2/4*AX23*ABS((1-2*(0.175+AV21)*AW17/(BA9+2*0.013-0.002)))

the pressure is reduced by the friction term, 0.175, which is reduced by the case taper and the brass surface area.
In the 375 H&H example i gave earlier, the brass friction reduction in bolt pressure is
78.86% or a hair less than 6900psi.
The case taper for the H&H is -0.0149 in/in but for most of the magnums in my file, is
-0.0060 in/in. So, the H&H case is less "grippy", than say the 416 Remington or a 458 Lott.
For the Lott, the psi reduction is 84.36%.
As i said, i used to use the QL bullet base pressure, which varies around 85% but this is not related to the friction, just the powder burning, so I went to a bit more physics.

Mark A Ouellette · Mar 5, 2026

Jefferry404 said:
I was suprised at the reduction. In the pass i used the QL bullet pressure as a way to model but then went to the friction form below:

PI()*AW24^2/4*AX23*ABS((1-2*(0.175+AV21)*AW17/(BA9+2*0.013-0.002)))

the pressure is reduced by the friction term, 0.175, which is reduced by the case taper and the brass surface area.
In the 375 H&H example i gave earlier, the brass friction reduction in bolt pressure is
78.86%. The case taper for the H&H is -0.0149 in/in but for most of the magnums in my file, is
-0.0060 in/in. So, the H&H case is less "grippy", than say the 416 Remington or a 458 Lott.
For the Lott, the psi reduction is 84.36%.
As i said, i used to use the QL bullet base pressure, which varies around 85% but this is not related to the friction, just the powder burning, so I went to a bit more physics.

This may explain why belted magnum brass stretches and breaks just ahead of the belt!
The body of the brass sticks to the chamber with high pressure pushing back the head of the case.

Jefferry404 · Mar 5, 2026

Wyatt Smith · Mar 6, 2026

Mark A Ouellette said:
I appreciate all the thought concerning brass friction in chamber reducing bolt thrust, but how big a factor could that be?

Could it be equal to 1,000 psi directed outward to the chamber rather than backward to the bolt?

I read about a man who was loading a Remington 700 in 308 pretty hot. The cases were sticking so he lubed them really well thinking it would help extraction, after the first shot a locking lug broke.
I would guess that brass friction is pretty important if this story was true.

Choupique · Mar 6, 2026

Could it be equal to 1,000 psi directed outward to the chamber rather than backward to the bolt?

Pressure doesnt work that way. 1000 psi in the case means 1000psi on every surface exposed to it. The way described earlier is one way, and it shows a very significant reduction in bolt thrust due to case wall friction. That pressure is also equally applied to the inside of the case head.

Its a complicated event to quantify.

fourfive8 · Mar 6, 2026

Only one way to answer the question as posed in the OP. Pressure gauge/sensor on chamber and strain gauge on bolt face/breech block locking interface (s). Then, load up until mechanical failure. Compare/analyze data from gauges.

Mark A Ouellette · Mar 6, 2026

Choupique said:
Could it be equal to 1,000 psi directed outward to the chamber rather than backward to the bolt?

Pressure doesnt work that way. 1000 psi in the case means 1000psi on every surface exposed to it. The way described earlier is one way, and it shows a very significant reduction in bolt thrust due to case wall friction. That pressure is also equally applied to the inside of the case head.

Its a complicated event to quantify.

Thanks but I understand that pressure is constant in a closed cell pressure vessel.
My post asked if brass friction was a small factor, such as 1,000 psi?

Mark A Ouellette said:
I appreciate all the thought concerning brass friction in chamber reducing bolt thrust, but how big a factor could that be?

Could it be equal to 1,000 psi directed outward to the chamber rather than backward to the bolt?

Jeffery 404 eplained in it!

Jefferry404 said:
I was suprised at the reduction. In the pass i used the QL bullet pressure as a way to model but then went to the friction form below:

PI()*AW24^2/4*AX23*ABS((1-2*(0.175+AV21)*AW17/(BA9+2*0.013-0.002)))

the pressure is reduced by the friction term, 0.175, which is reduced by the case taper and the brass surface area.
In the 375 H&H example i gave earlier, the brass friction reduction in bolt pressure is
78.86% or a hair less than 6900psi.
The case taper for the H&H is -0.0149 in/in but for most of the magnums in my file, is
-0.0060 in/in. So, the H&H case is less "grippy", than say the 416 Remington or a 458 Lott.
For the Lott, the psi reduction is 84.36%.
As i said, i used to use the QL bullet base pressure, which varies around 85% but this is not related to the friction, just the powder burning, so I went to a bit more physics.

How can the mechanical stress exerted by DG cartridges on the action be estimated? Peak pressure alone is not a solution

Accidental Villain

Choupique

Jefferry404

BlackRhino

Nhoro

Jefferry404

Huvius

Choupique

C.W. Richter

Jefferry404

Mark A Ouellette

Jefferry404

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Choupique

fourfive8

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