Remove the broken/ weak spring with loops of dental floss.

Then unscrew the stubborn screw.

Impact driver if you have one.

When you had your unexpected "Over Pressure" you did more to that bolt assembly than just breaking an extractor claw.  The bolthead for 2A & 2A1 were typically made from malleable steel with only the face being heat treated. Even though you have stated that you had test fired the rifle, "After The Fact" and everything worked accordingly, you are still playing with a damaged rifle component. The assumption here being that you have, in the literal sense of the word, "smashed" the bolthead to the point that it has soldered/staked itself to the screw...

You ever put a penny on a train track?

Your bolthead was the penny and your over pressure was the train. 

That screw might be able to move back and forth but, because of the extreme pressure it was put under, both the screw and the hole it is in are now shaped like an oval.  You just can see it.

Between the face of the bolthead and the lug recesses in the reciever, a space of approximately 4.25 inches and a diameter of less than 0.0580", your bolt assembly was hit with over 20 plus tons of forced energy that had nowhere to go except through the bolthead and then the bolt body. Do yourself a favor and contact BRIAN DlCK @ http://www.bdlltd.com" rel="nofollow - www.bdlltd.com and explain what you have and what happened. Explain what you are attempting to do as well...

 

If you know that your load was an overpressure, hopefully you know what the load was (unless you perhaps mistakenly double charged pistol powder with cast bullets or an unknown error you can't quantify).  Did you pull any bullets from this load to attempt to identify what went wrong?

Seriously, guy, its time to let it go. You're seeing many glaringly obvious signs of serious material damage.

I would not go any further in good conscience. You are playing in a field where ego has triumphed over good sense.

Whilst the untimate load is relevant - it is far more related to the almost instananeous 'shock load'  - like a hammer hitting a nail but a 'multiple' of many, many times force.

As a minimum the bolt should be scrapped and the rifle body given a serious 'looking at' looking for any signs of stress or stress cracking especially around the body locking lugs.

Personally I'd scrap the rifle - I'd never trust it again.

You have played Russion Roulette and now the risk has increased from 1 in 6 to 1 in 5 - do you know what the next round will do - even a 'normal' round may now be too much for the stressed body.

The Piezo peak pressure is recorded at a very high rate, so as to capture the peak (maximum) pressure in the chamber.  There's not enough inertia in the bolt and receiver and the load doesn't occur fast enough to prevent it all being reacted at the bolt head (some might be taken by friction of the case in the chamber). 

Curious tho, an issue he believes is due to a gas check?  Perhaps one got stuck in the bore?  I've never heard of this problem, there are numerous published loads for case lead bullets with gas checks in the .303 and other bottleneck cartridges... 

The original posts stated that the case came apart. Not separated,  apart. So the inertia was there in the form of a sine wave, starting in the chamber working backwards with the only damper being the bolt assembly first and then the lug recesses in the reciever.

For reference only: Your average stripped and used No4 bolt body is approximately 5.555" long. The one that I ruined measures in @ 5.415". The fact remains that, the damage is there, will always be there, and will not go away by simply wishing it away or swapping out parts. Your 8800 Piezo number is only correct to a degree as well.  There is also the amplification of the pressure wave as it is moving. Taking into consideration the actual square inches of surface the bolt body has and using the original oiled proof test numbers, the face of that bolt head was hit, although briefly with over 25 tons of highly forced pressure. No different than a hydraulic ram. Knowing there is a difference between tonnage in pressure and actual weight. The numbers are still there regardless. Like the difference between a ton of bricks and a ton of air. It all adds up to the same number, 1 ton. 

It's academic at this point, the damage appears to be there, but just interesting to see how large these loads are, right in front of your face!  

& with that consensus of educated opinion I'm gong to put this thread to bed.

Apologies to the O.P. but there may be those less experienced who will be reading this & I'd hate to think we as a group, even inadvertently set some newbie off on a road knowing there's a "dead mans curve" waiting just around the corner.

I'm not going to delete it because there's a lot of good information & it is if nothing else serving as a cautionary tale to others about overloads. & reading bold clues of impending failure of an action.