Am I being silly?

[Kevin Peacocke]

Apologies for the boring technicality of what follows. Skip by all means.
Been doing a bit of research into cartridge brass and it's properties, especially Young's modulus. I think I know know what is happening and why. See the curves below (courtesy Physics Stack Exchange, not for brass, but illustrates the point). When you fire the forces are so great that the brass will go instantaneously through it's elastic limit and passes straight into plastic deformation, that is the curved top bit. That is why you can fire-form cartridges. If it is on the rising part its ok, if it passes over then its all downhill from there until the break point at the end of the curve. Note you have far less latitude once the material has been work hardened, see the second steeper curve. Even though the extension begins later it ends earlier and the curve part falls off the cliff sooner and more dramatically. In a nutshell, reloaded brass needs to be quite closely contained in a tight space or you will eventually push it over the edge of the cliff. The greater the head space, the sooner this may happen, even after one reload in my case.
So what is the solution?
1. Bring the head space back into tolerance if you can.
2. If this is impossible use only new brass so you are always on the pre-worked curve. Then discard the brass.
3. There is the option theoretically to anneal the fired brass to restore it's ductility and get back to something like the first curve before reloading. However this is dicey with a headspace issue because plastic deformation will certainly have occured in the first firing anyway and all of the next deformation event will happen at the thinned point created first time around. Young's modulus is about extension per unit length, and if the thinned band is all of say a millimeter or so, then the same few thou of movement due to head space will be happening at that 1mm - result being a split case.

One more thing I have come to realise is that forward pivoted doubles will have some flex, and of course the top barrel in an O/U sees more of it just taking the geometry into account. Now add the extra mechanical advantage of the top barrel firing event trying to swivel about the pin and you see it exacerbates the problem. Cure? A Greener bolt or some other form of top lock up, rising bite, doll's head, etc. Only use modest calibres in O/U especially small framed ones obviously, and never load a hot charge.

 

[IvW]

For a cartridge that headspaces on the Rim I would think it is non negotiable to get the headspace sorted out, which means a new set of barrels as I doubt the existing ones can be reset further back and re cut.....

 

[Kevin Peacocke]

There is one machining option, but you would need to be extremely careful and accurate and have the correct reamers. You cut the flange recess even deeper to about 3mm. You then insert a tight fitting sleeve to come right back to the barrel face and soft solder it in place. Then you very carefully re-ream the cartridge profile to only cut the taper into the new sleeve, no more. Then finally you re-cut the flange recess, this time correctly to give one thou recess maximum, relying on the barrel to breach distance for safety, which is 4 thou in my case.

 

[IvW]

What about the chambers that are cut to deep? Or will you rely on neck sizing only?
You will then be fire forming with each shot...much like firing 375 H&H ammo in an AI chamber. Which will also result in loss of performance. 2400 fps in the Flanged magnum is the perfect speed.....
How will this affect regulation?

 

[Kevin Peacocke]

What about the chambers that are cut to deep? Or will you rely on neck sizing only?
You will then be fire forming with each shot...much like firing 375 H&H ammo in an AI chamber. Which will also result in loss of performance. 2400 fps in the Flanged magnum is the perfect speed.....
How will this

What about the chambers that are cut to deep? Or will you rely on neck sizing only?
You will then be fire forming with each shot...much like firing 375 H&H ammo in an AI chamber. Which will also result in loss of performance. 2400 fps in the Flanged magnum is the perfect speed.....
How will this affect regulation?

The chambers fortunately appear to be fine, it is just the flange recess. They obviously cut the chamber first, then the resess with a second reamer and that's what they buggared up. Even if there was some frontal fire forming it is well within the allowed expansion. The front of the cartridge will then rest on the formed shoulder, no problem though.

 

[IvW]

Ah ok I initially thought the had cut the entire chambers too far forward....that problem may well be fixable....I will make some enquiries...that of course is if VC do not come up with a solution ...or I will buy the rifle from you....

 

[DWB]

I again want to say investigate the old .303 Brit method of an o-ring or piece of soft soldering infront of the rim. This causes the shoulder to move forward and not the head of the case to move rearward. Then necksize from there. Sure it will buy you a few extra shots.

 

[Kevin Peacocke]

The chambers fortunately appear to be fine, it is just the flange recess. They obviously cut the chamber first, then the resess with a second reamer and that's what they buggared up. Even if there was some frontal fire forming it is well within the allowed expansion. The front of the cartridge will then rest on the formed shoulder, no problem though.

As to regulation, no change at all, still a 300 grain bullet at 2400fps.

 

[Kevin Peacocke]

So the only remaining question is, for me anyway, why do the cases always split in the same place? If you look at the cross section of one of my once-fired cases, the thinning band is just at the transition point between the thickening wall towards the base and the thinner paralled section towards the shoulder. So why didn't the thinning band occur further up the parallel section? The reason as my gunsmity pointed out to me is that the massive pressure more easily expands the thinner parallel section against the chamber wall where it is locked against movement by friction. The base will be less tightly held and can move a smidge, hence the expansion at the transition point.

 

[WAB]

It still doesn’t explain why the rifle opens on firing at times. Failure of the brass doesn’t seem like it would change the pressure or recoil pulse. Have you heard from VC? They seem active on here. I would think a PM would be effective.

 

[Wyatt Smith]

It’s not very a scientific, but I have never seen a case head separate anyplace else.

 

[IvW]

It still doesn’t explain why the rifle opens on firing at times. Failure of the brass doesn’t seem like it would change the pressure or recoil pulse. Have you heard from VC? They seem active on here. I would think a PM would be effective.

Wit the the cartidge sitting forward as the firing pin activates the primer it slams back to breach face. Second fire cases are already damaged and then after the reloading the case(resized but already weakend) seperates causing much increased pressure which causes the action to open. That is also why it is only the once fired cases that are head seperating. Remember this is a O/U double so is designed to operate at lower pressure so any pressure issues will cause problems. Therefore it should be fixed before firing again and causing permanent damage to the action or shooter.

 

[Kevin Peacocke]

Yes, no case split, no breach opening. Do new cases ever split? I have never heard of this, and surely the tens of millions of rounds fired in military use from ill fitting rifles like AK47's support the integrity of new cases.

 

[Hogpatrol]

Yes, no case split, no breach opening. Do new cases ever split? I have never heard of this, and surely the tens of millions of rounds fired in military use from ill fitting rifles like AK47's support the integrity of new cases.

I would surmise AK's are all firing steel case ammo.

 

[Hogpatrol]

There is one machining option, but you would need to be extremely careful and accurate and have the correct reamers. You cut the flange recess even deeper to about 3mm. You then insert a tight fitting sleeve to come right back to the barrel face and soft solder it in place. Then you very carefully re-ream the cartridge profile to only cut the taper into the new sleeve, no more. Then finally you re-cut the flange recess, this time correctly to give one thou recess maximum, relying on the barrel to breach distance for safety, which is 4 thou in my case.

All this and you'll end up with an expensive, jury rigged rifle that won't be worth half of what you paid.
Besides that, you'll need the same reamer that the manufacturer used. They aren't all the same, even in the same cartridge. Considering liability issues, I would bet if the manufacturer got the barrels returned, they'd go in the scrap can. This is the old, first time firing, clamp it to the bench, get behind something and pull the trigger with a string scenario.

 

[IvW]

Brass and steel cases have been and are used in the AK 47....

 

[Shootist43]

Kevin, after all that has been said and done and you still have no physical injuries I'd send that rifle back to the manufacturer. Have you contacted VC yet? Emails can be sent with little effort and should result in a permanent fix, even though it may take a while.

 

[IvW]

He is at the take a while stage......

 

[cls]

For what it's worth, This is a new rifle and as such a reputable manufacturer should step up and fix the problem. The owner should not have to come up with a solution for a problem that isn't of their own doing! Seems to me that VC is being awful quiet when they are on this site regularly. At present I wouldn't take one of their firearms even if it was free with a case of ammo. Just my 2 bits.

 

[Kevin Peacocke]

Kevin, after all that has been said and done and you still have no physical injuries I'd send that rifle back to the manufacturer. Have you contacted VC yet? Emails can be sent with little effort and should result in a permanent fix, even though it may take a while.

Yes, contacted them, nothing back yet. I think maybe tomorrow they should be back from holiday.