You can get a reading for the 5 groove groove diameter by gently rolling the slug between the jaws. This is delicate and perhaps not as precise as one would like, but can generate a reasonable measurement. I have tried removing the lugs left by the grooves from the slug, and trying the same trick, to attempt to get a bore dimension, but don't really trust the results. I think the best way to get a better sense of bore diameter in a 5 groove is to use plug gauges. The least expensive source I've found is w ww.meyergage.com. I don't have a set for .303, but do for .223 and .30, that I use to dial in a barrel for chambering.
Reloading the 303 British with 308 bullets.
- Thread starter snowhunter
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