simulation data please :)

[bmacconaghy]

This is my first post on the hide, so I hope this isn't going to be too out of place. I've been reading about reloading, optimum charge weight, optimum barrel time, etc... And I thought it would be interesting to simulate the physics of a rifle discharge with a finite element model. If this has been done before please tell me where to find it! I put one together in Comsol the other day, but I don't have a good pressure curve; I just kind of picked some numbers and threw some equations together. I think it would be interesting to see a multiphysics time dependent linear elastic and acoustic simulation to capture the traveling wave of the discharge as it reflects back and fourth down the barrel. The preliminary work I've done demonstrates that this is occurring, but there are other structural waves and surface waves to worry about. Some of these may be due to the pressure curve that I'm using. I would like to use an existing load that someone has determined to be accurate and muzzle velocity stable. It seems like that would be good empirical data to compare the model against.

What I need:

your barrel material:
barrel length (cartridge base to crown):
cartridge:
QuickLoads or measured pressure vs. time data:
barrel time of bullet:

If possible it would be nice to work with a known accurate load and a different inaccurate load in the same rifle, but that's not necessary for a first stab at it. I think it would be best to start basic, and if we get some good results we can work together to get more sophisticated. I appreciate any help the snipershide community can offer.

Thanks,

Brian

 

[Boogaloo]

I love science like this, but am not equipped to perform the calculations myself. I was never a math whiz, and it's something about myself that I wish was different. I truly do marvel at guys like you, who's brains are wired for this type of brainiac science.

Anyway, here's one to start with, I have a few more, but ALL will be from 24" barrels since all 3 of my precision rifles are built to 24".

Barrel Material: Stainless
Barrel Length: 24"
Cartridge: 308/208 AMAX @ 2580 (avg) FPS.

Here are some pics with data that may help:

 

[bmacconaghy]

This is great! I have the computer working to render a vid of the initial results. I started with a 24 inch barrel, because that's what my 30-06 has. But the pressure curve is something I made up. I'll try to post the results when I get it in a proper format. I can easily change the chamber to 308, but I doubt it will show a marked difference. Time will tell.

Boogaloo, can you save the pressure curve in a spreadsheet or text file? Thanks for sharing the data! I'm excited!

 

[bmacconaghy]

It seems like there are three different Max pressures and at least two different barrel times shown in different locations in the pictures of quickloads results. Can someone offer some insight into quickloads please?

 

[bmacconaghy]

...

 

[bmacconaghy]

Here's a video of the preliminary simulation with an unrealistic pressure curve. I hope to implement the realistic data soon. This video is a short clip from the simulation which illustrates the dynamic wave patterns produced and the traveling wave reflecting from the barrel muzzle and beginning to propagate back toward the action. The chamber is a 30-06 and the barrel length is 24 inches. I'll take more care with the details of the model next time, but for now it's interesting to see the material distortion (first principal strain) propagate along the barrel and reflect like the rings of a slinky.

 

[woojos]

Nice work! I'm interested to see how this turns out.

 

[Boogaloo]

I am wondering how you will account for the differences in barrel profile? My non mathematical brain can't help but think that larger diameter barrels will not flop around as much as thinner profiled barrels. The other thing I wonder about is how much effect would a barrel with a thick breech section that tapers less have than a barrel with a standard breech section that tapers more? How do you account for that?

Finally, I wonder if there is a way to determine if strategically placed "dampers" would positively impact the outcome? I see guys at the range with hot rod small bore rifles that have dampers that they can move forward and aft to "tune" the barrel. Can you simulate those things?

 

[bmacconaghy]

I suspect that the barrel dimensions will come into play as well as the action rigidity and how the force is coupled into the stock. I can make the barrel profile whatever I want and a damping mass can be simulated as desired to see how it affects things. I chose to start with a straight barrel profile for simplicity, but it's very easy to change that. What barrel profile are you using, Boogaloo? I'll make the model match that... Also, how's that spreadsheet coming?

I think the way the force is delivered to the shoulder will be very dramatic. Normal stocks couple to the base of the action, so there is a torque which whips the barrel, but rifles like the tubb 2000 or similar tube guns push straight back more effectively. I'm intending to simulate this dynamic once I have a working simple model. Any suggestions are welcome.