So we have the ammo

Yes indeed we had a box sealed and full of 20 rounds of 7mm Mk1z (thats nitro cellulose powder) and we had to open it. This caused consternation in some quarters. One forum even went so far as to call me a vandal.
My response? I cant fire it inside a box can I!
Yes my friend had won the argument we had decided to have built a brace of rifles in .280 British (as the Proof House decided it was called) and set about procuring a handful of suitable donor rifles.
We had looked at previous efforts and found that Lewis Potter and one other had rebarrelled at least one Ruger No1 in this caliber and they very generously shared their load information which unfortunately was mainly based on a 120 grain load but it was a very useful starting point and we were very grateful.
I will be reproducing the load tables here (later on of course) and also the test results even the ones which highlight all of the errors I made along the way. If I chose not to share my mistakes then you may end up making those yourself.
Somewhere along the way we decided that to save time we would work on ammunition production whilst the rifles were being built. Concurrent activity and all that!
Dies were sourced from Redding Dies in the USA and case conversions were investigated.
The obvious place to look was the history books.
As the initial offering to the Nato trials had failed due to anaemic performance the final version was based upon the same T65 case as the US were using in their 7.62 x 51 mm offering. Sadly the US wouldn't allow the improved .280/30 as she was known to be entered into the trials and the US offering was deemed to be the winner.

The image above shows the 30-06 Springfield on the left and the 7.62 x 51 on the right with the British offering of .280/30 or 7x43mm in the middle. The ammo all share one character, the case head dimension is sufficiently close enough on all three to remove any need for bolt alterations in our rifles.

So two Remington 700 rifles were acquired at auction. They were in calibres which would mean a shared bolt face. .22-250 and .243, Remingtons were chosen because of the range of spares and options available as we go down the road of building these rifles.

Next was selecting a suitable riflesmith capable of producing a decent job on these. We had a number of options but our pockets weren't sufficiently deep enough for the best so we looked at smaller businesses. A friend overseas had some work done and recommended a smith down in the south and my oppo Paul had ordered a 6.5 Grendel on a CZ527 action from Riflecraft. The difference in the end came down to cost.

I wish then I had spent the extra hundred pounds. Pauls CZ had a terribly tight chamber and the Smith wasn't as communicative or helpful as he should have been. All of these should have warned me but Pauls Grendel was impressively accurate.

We left the rifles (along with another project rifle) at Riflecraft, with four rounds of ammo for them, 2 for proof testing per rifle and also for reamer measurements and walked off.

Then we got stuck into brass conversion.

Brass conversion, now there is another tale.

Rather than repost the original from The Firearms Blog I thought it would be more enjoyable (and easier to spin out) if I went through each stage of this journey, one post at a time.
I had always had a certain level of interest in the rifle and cartridge ever since I was able to read and able to get hold of historical papers.
I cant recall offhand the date but sometime in the last ten years or so when the HBSA was still meeting on HMS Belfast I was fortunate enough to attend one of Tony Edwards many and informative lectures. Sadly as he explained at the end this was to be his last and no published work would come from it (sadly Tony died not long after) but he was however as ever helpful and happy to answer our questions.
I should explain that I had taken a guest to the lecture, my very good friend Paul.
The lecture has been recorded at least in slide format here I thoroughly recommend reading any and all of his lectures where available. I have all of his published works (I think and hope) and will grab any more that I find.
The lecture was on the development of post war (WW2) British Self loading rifles which really starts at about the beginning of that war.
Paul was enthused as was I and we pondered what possibly we could do to resurrect the cartridge and rifle.
Shortly after that Forgotten Weapons did a series on the EM2 and I sadly missed an opportunity myself to attend a shoot where one was in use.
Anyway as they say thats all in the past.
I was then a fairly regular visitor to various firearms auctions around the country and one item appeared in the sealed bid sale that caught my eye.
This was a box of 1970 production 7mm Mk1z ammo by Radway Green (Later to become part of Royal Ordnance and even later Bae), this was produced according to various reliable sources for use in the 1970's decade of ideal calibre trials (won of course by the Belgian SS109 5,56 x 45) and had been a small line at the factory kept especially for such development work. The brass was also used in various forms apparently to deliver 6 + mm projectiles as part of the trials.

As luck would have it I won the auction and collected my box of ammo still sealed from the auctioneers.

Yes thats it sat on the firing point, more of that later but the ammunition inside was 140 grain ball with a purple tip but of the powder we knew nothing. Later research hasn't given us very much along those lines either.Well thats enough for now, some of us have a bit of work to be getting on with!