Nelly is only 4yo.

so when he is fully matured at approx 7/8yo,when he has bulked up (not fat

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He will then be a very nice show cob indeed.Having 10.5" bone and being of correct height,with fab markings and great confirmation to grow into .
I personally love the coloureds and the fact that they get to keep their feathers,Nelly had amazing feathers that got commented on at every show,but he is not marked well enough to compete in coloured classes (he only has a huge white splash under his belly)
The "show cob" classes are split into two different classes "lightweight" and "heavyweight" ,as in the link LL posted,it even says that.

CF ive no idea on the usual breeding of these types,i suppose it must be a bit of pot luck,with the height stipulations

I suppose we will see how good a "show cob" he turns out as he matures and gets older.
This might be a bit better pic of Nelly,he is in 6ft 6 rugs and a 6" bit.i dont like to keep him fat either.