Reloading .303 British : Chamber Space

Test for it? (assuming you reload again) take a fired case. Gently punch 3 dimples equally spaced (more or less) around the neck. Manually push a bullet in backwards. Just enough to hold it. Now pull the trigger & hold it & slowly ease the bolt to close with your test in the chamber, making sure the bolt closes fully.

Carefully pull it out without letting it fall.

Measure the overall length.

Make a not of it.

Now compare that reading with good known readings from newish barrels.

If yours is a good bit longer (not tiny amounts) you throat

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Rather than gently punch 3 dimples around the case neck
couldn't I use my lee collet die set that I have never used to size the neck ?