Not sure if it's the same one or not, but this is an earlier pic (8/23) and they are all about the same size, but a little bigger now.
View attachment 14964
I'm not sure what "big" is for a chestnut bur. They seem to be growing and I have 3 of them in a row about 25 feet apart from each other in this location and these burs seem to be growing so I'll be pissed if i don't get at least one nut out of them! I actually have burs like this on 2 of the 3 trees. I'm not expecting multiple seeds in a bur, but I better get at least one! They a certainly larger than a single buckeye for reference and the outer portion of the spines is about the size of a fresh green walnut (husk and all).