Neck bush size when using a Mandrel Expander

[Gungrinner]

I was just wonder what bush size I need for my Redding type s die. I want to use a Sinclair .307 Expander Mandrel on 308 lapua palma cases? I have a .337 bush and was wondering if this would be ok. I just wanted to know so I don't have to pay for postage twice if I order the Expander Mandrel and bush. Thanks

[Brillo]

I’ve used a .336 since the year dot.  A 334 is too much so I’d suggest a .337 is too little.

[palo]

I also think 337 is to little. 

I use a forster full length die with the neck honed to .335 and then I use a .307 mandrel.   It works very well and  the mandrel is working very little. A .336 bushing will probably be ok but it might be safer getting a .335 .

 

[Leeman]

You'll only know for sure when you measure your brass with a seated bullet, otherwise you're just guessing.   Measure a dummy round and subtract 2 thou if using neck turned cases, if not turning necks I'd assemble three dummy rounds and take the average, then subtract two thou.  Having said that I've used cartridges with 1, 2 & three thou tension at various times so IMHO and for my rifles, the exact tension wasn't that important, or at least not as important as say charge weight and bullet seating depth.  Some people recommend buying two or three incremental sizes to experiment with anyway.