I have been some more research before ordering my Reloading Press and Kit.
As they say "nothing new under the sun", so I was hoping to acquire some knowledge from fellows more experienced than I:
* Is the Blaser mag length the limiting factor in attempting to seat GS Customs 50 thou off the lands? (As I do not have gun, bullets or equipment to hand, this may be impossible anyway as the minumum seating might not be achieved)
If the mag is not the limiting factor, then I will need to add some more gear to my shopping list. I am already buying a RCBS Precision Micrometer so I can do partial length resizing and knock the shoulders back 4 thou - this little gadget apparently can help a little with seating depth but is not particularily good as it does not use the actual bullet considered.