303 & oversized barrel

You mentioned "at its widest" ?
If you slugged the barrel, your reading will be at the narrowest?
If you have mono bullets turned for widest part of the barrel, what will come about at the narrowest part of the barrel when mono gets there?

Me?, I would go buy a box, loan 10 of .312" 174 gr bullets and test that first. I would then shop around for cast .314 " bullets. If that barrel is a .316" you never going to be really happy, just too many hassles.

Treeman, the slug measures 8.05mm at its widest. This means that the bullet should measure 8.05mm in diameter to seal properly, or do I miss something?

A narrower bullet (.312") would just rattle down the barrel?

I got some milsurp rounds from an old bisley shooter. Will try them and see what they do. It should give an idea of what is possible.

OK Folks, chance to laugh in relief.

My vernier is out by 0.1mm - sincere thanks to Johan Kriek from Kriek bullets.

It means that the actual measurement is 7.95mm and a standard .314 bullet should do just fine.

Good evening Folks,

The 303 barrel slugged out at 8.05mm (.316") at its widest.

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The above , to me meant the barrel at its widest, just a misunderstanding of info relaid, I thought you had measured in some other way perhaps at each end and meant that you had found the barrel to be at .316 - the barrel slugged out and not the slug measured at. The slugs measurements are the complete opposite to what I was stating.

OK Folks, chance to laugh in relief.

My vernier is out by 0.1mm - sincere thanks to Johan Kriek from Kriek bullets.

It means that the actual measurement is 7.95mm and a standard .314 bullet should do just fine.
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my rifle will shoot a round nose .312 bullet at .5" group - 100 m. Any other Jacketed bullet is almost A4 page grouping.
303 Cal .312 174 gr InterLock® RN Item #3130 | 100/Box