Orpingtons can be very large birds - especially if you've got them from a breeder or if they came from English bloodlines. The imported English bloodlines look like basketballs with heads. They're extra fluffy. I've also seen some hatchery birds look thin like RIR. They're smaller and bred for decent egg production, so it's not all bad.
I allow my flock to free range but they also have a feeder always filled with commercial feed. The birds prefer to find treats in the yard and go to the feeders if they find nothing better. Since it's always there, they don't overeat the feed.
Here's a pulet on the large side (almost 9lbs in the pic) She grew to a little over 10.
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This is more a normal sized orp pullet
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Here was our all-time fav roo. Don't let the big size fool you. He was a gentle, old, soul and the best flock leader we ever had. We actually had bigger boys, but this guy was the boss. He was also gentle and allowed the kids to simply pick him up.
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It takes a long time for an orp to reach full size and fill out (about 18 months)
Here's a 4 mo old baby cockerel. They get tall but are mostly bones
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These are my laced orps. You'll see what I mean by "basketballs with heads"
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These 2 are only 4 months but I like their shape so far. They're mostly fluff.
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This one is 7 months & just started laying. She's fluffy AND heavy.
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I hope these pics help.