8x57r to 303 British

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erikyaremkewich

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Squamish, BC
Would it work to neck 8x57jrs brass down to 303 Britishor neck 7x57r up to 303 British? I seem to remember reading somewhere that 303 British can be necked down to 7x57r. Have any of you tried this conversation?
 
I have successfully sized down 303 to 6.5 x 57r. The 303 neck easily sized down in a set of 6.5 x 57r dies. I then fire-formed the brass.
This was for my Drilling. The 303 cases blew out to the 6.5 chamber dimensions, except near the base where the web metal was too thick. The rims on both my 303 brass and some necked down 7 x 57r brass that I had, where too thick for my gun, so the extractor could not remove them. I had to knock them out with my cleaning rod.
I think the extracting problem may be individual to my 100+ year old gun. My 6.5 x 57r marked brass extracts fine though.

I have many hundreds of 303 brass, so I am not tempted to try forming 303 from 8 x 57r, which tends to be scarce.
 
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The 8x57jrs has a larger base. This would need to be reduced to allow the brass to be chambered in 303B.
The rim is also thinner. It stands to reason this would affect headspacing in the 303B chamber.
A lot of work considering the readily available 303B brass in comparison to the scarce 8x57jrs.
 
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