243 Fury and 243 Fury AI

[Chris in TN]

With sustained 80k psi you are not going to get a catastrophic failure, if anything youre going to get bolt set back.

I'm assuming this would show up as a growing headspace issue or be really obvious when you went to rebarrel. Correct?

 

[Tanner]

they never leave the chat, the case necks split.

That’s pretty cool. How many firings before you’re splitting necks?

 

[Waltersobchak]

That’s pretty cool. How many firings before you’re splitting necks?

with 16 inch 22 creed shooting 88tmk's at 3100 FPS, two firings. With 6 creed, 109 elm doing 3175 out of a 22 inch barrel, 4-5. With 308, 212 eld doing 2500 fps out of a 16 inch barrel, 10 firings. with 8.6 blackout, 10+

 

[z987k]

Honest question, and I'm not asking to be critical - the numbers you're posting here are fascinating.

I'm not afraid of 80kPSI. What I'm afraid of is 80kPSI in a rifle designed for 65k.

From a metallurgical standpoint - I am not an engineer but I kinda worked in that world for a while and there was a very common rule of thumb that a part or gadget that would fail catastrophically at, say, value X, would likely run forever at value 1/2X and the engineers I worked with would spec things to run at that 'forever' load point but in reality they often exceeded it and always got away with it, until they didn't, which usually occurred after the original engineer had retired and it was someone else's problem. If we apply that to rifle actions we would want to design a rifle action that would hold together up to perhaps 130kPSI in order for it to 'run forever' with 65kPSI ammo. Or, in terms I used to play with a lot, my old Ruger Blackhawk was, per John Linebaugh, good for about 65kPSI before the cylinder failed, so in theory we could run 32kPSI loads in it forever, and when I went through a phase of being enamored with big bore handguns that's what I did. And, yes, I exceeded that a few times, likely pushed it to nearly 40kPSI a very few times, but stopped that because there's nothing I could really do with a handgun at 40kPSI that I couldn't really also do just as well at 23kPSI. But I digress.

So, to apply the above to your project here: If it's true that the Tikka is a true 65kpsi action, then what you're doing is somewhere on a sliding scale between 'run forever' and 'suddenly gernade on you'. It's also possible that the Tikkas have been failure tested and are stronger than I assume. If they'd hold together up to 160kPSI then I'd be fine with the 80kPSI figure, assuming primers held and you don't get gas in your face.

So....either a) the rifle is rated to handle the pressures you're seeing, or b) you're at pressures that won't create instant failures but you're turning the receiver into a consumable with a finite life. My question is, do you know which it is, and if the latter, how many rounds before you cease to trust the receiver and retire it?

I'm not asking to be critical and I'm not asking from the standpoint of looking down my nose like I'm smarter than you. I think the project you're working on is incredibly neat. I'm simply wondering what the long-term implications are for the integrity of your rifle action.

You need to specify where you're actually concerned with the pressure. Do you think the bolt can't handle it? The action where the bolt lugs ride? Or do you think the chamber/barrel can't? Very very different things.

You can't just say X is an action that can handle Y. Actions have multiple parts that are all subject to different forces.

We can show through math how a 308 bolt face at 80kpsi has almost the same bolt thrust as a magnum bolt face at 65kpsi. It seems everyone that asks this question doesn't know that bolt thrust has the radius of inside diameter of the cartridge as a variable. And R is squared, because it's the area of a circle.