Can anyone give me a clue to what is causing the neck/shoulder split in new brass?
Details as follows:-
W-W super , .264 win mag brass (new). Not the neatest looking brass I've come across!
CCI magnum primers
52.0g H4350 (Start grains = 51.1g)
Hornady 129g SST
3.322 OAL (OAL to lands is 3.358)
The same set-up seems to work with Hornady 129g SP to give 2880fps and sub minute accuracy out to 300m. I've fired over 50 rounds with this load without a problem. Not a lot, but three from three split when using the SST.