Sinclair chamber length gauge finger-inserted into cut-down 6BR case. The 6.5mm version is on the right


checking initially that all sized cases in a box would still chamber freely. I always run a few sample cases through the gauge at the start of a resizing session too to ensure the die adjustment hasn’t somehow slipped.


I wonder if this phenomenon is a historic legacy with the BR with die-makers catering for minor variations in chamber lengths and/or the die shoulder position set on the ‘aggressive’ side assuming that brass will be re-formed from .30 UBBR or .308 Win parents. In any event, creating excessive headspace like this not only reduces case life drastically but can have safety implications in extreme cases. It will also affect


group sizes and give false (flat or standing out proud) fired primer readings.


Talking chamber lengths, I did another check when the rifle had first been rebarrelled, one that isn’t confined to 6BR – I used a 6mm cal. chamber length gauge from Sinclair to check on the length of the chamber’s neck section. The gauges are available in all calibres and are little leaded steel bullet diameter cylinders with a button or mushroom head on one end. You have to sacrifice a case, sizing it and trimming a tenth of an inch or more off the neck before partly seating the gauge in the case-neck with the press and seater die. You then chamber the


Target Shooter 59


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