case head expansion

mikeystew ........

The British .303 needs to headspace on the rim, and it's best to have .006" (preferably less) clearance between the face of the bolt and your cartridge. The first firing blows the case shoulder forward, and this usually goes quite a long way. This causes case stretching, and it thins (and weakens) your brass just above the case head.

That's what causes head separations. When reloading the British .303 it's important to keep your chamber clearance (at the shoulder) to a minimum ....... less than .002" is ideal. If you do that ...... you'll never see a head separation.

- Innovative
 
And, if you remember not to use unknown count handloads, or those over three or four in any case, for match or hunting, case head separation in a .303 doesn't seem to be a big deal. Pain in the ... to get out - no biggy, just a nuisance - but I have never heard of anyone actually being hurt by a simple case head seperation in a .303. (Modest loads, which are more fun to shoot anyway, will prolong case life, as will neck sizing only.
 
On primer flattening.
The rounds loaded by CIL/Imperial/Dominion/whatever, were quite stout, or the primers were soft. Primer flattening was normal for factory loads.
It's also quite normal to have to discard a good amount of this brass, on it's first firing, due to incipient case seps. The one sided case stretch is also normal for this stuff.
Once you've gone through the bad stuff however, the brass lasts quite well. You can check for the incipient separation with a bent paper clip.
In my experience, neck sizing your 303BR brass regardless of manufacturer is key to long brass life, as is avoiding high pressure loads.
 
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