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Going from triangle to hollow does not take a lot of time and allows you to make some alignment adjustments.

You also have to be much more careful in aligning things if you hollow it by hammering ...

Are beer or other alcoholic beverages involved?
:)

I think the 4140 would work well. They are large enough that the rounding is not an issue. Most of what I do is on the tandle and the corner of the plate. You'd need to add a hardy or 2 for hammering...