Sir,
I salute your dogged lunacy. Most folk would go with a 2 kilo budget special from asda to test the water, but not you friend 13 kilos of shoulder straight off the bat!
Having read most of what has been on these forums, and blessed with a memory like a steel trap I do not recall anyone ever attempting such a monster shoulder. For your sanity next time out why not do a couple of 5kg bad boys and save yourselve the stress??
I know the answer because they wont be as "BIG!"
Fair enough, carry on

Cheers
Tiny