Valve Model Bounding Box vs. Custom Model BBox

I noticed that a lot of Valve’s models (like static and physics props) have a bounding box with “padding”. You can see this padding in Hammer viewport, mdl bbox turned on in the model browser, and seq. boxes. Custom models always appear to have a very tight bounding box that is flush with the mesh. I don’t understand how they’re able to achieve this. Example pictures:

Why is this important? The bbox apparently affects in-game calculations (that’s interesting!) and it provides clean, even spacing in Hammer for placing props, to boot.

Compile the modelsrc that Valve provides and the box is different from the compiled version they provided. Same also applies to decompiling and recompiling a model. I know there’s a qc command like $bbox, but I can confirm that only affects the model browser and it is an obscure qc that Valve rarely uses (according to VDC discussion). I’ve scoured search engines and forums for a while now unable to find an answer. I’m hoping that it’s just myself lacking the right search terms. Thanks for any of your input!

I don’t know the specifics of how the BBOX affects things either, however I can hitboxes within HLMV like so:

Also hitting generate QC copies to the clipboard:


Perhaps use coordinates generated from hbox and change it to BBOX?

Also on the talk page for BBOX on the valve developer wiki talks about it being some kind of old “hull” system thats no longer used.

$bbox is not the solution. It only modifies mdl bbox from the model browser, but it does not affect Hammer’s outlining box for the mdoel and HLMV seq. boxes.