I’m not sure what altimeter I had in mind when I designed the Au-198, but I definitely didn’t make it large enough to hold this:The fit into a BT-50 tube was close but not close enough. One reason: the plywood sled was too wide. (The purpose of this sled, as I understand it, is to protect the barometric sensor component on the bottom of the circuit board while allowing free air flow to it.) I cut a new one from a piece of scrap thin plywood I’d salvaged from a clementines crate. I also decided to reverse the hardware, which looks like a screw passing through a hexagonal spacer with a nut on the other side, but in fact is a hexagonal socket that was screwed to the sled plus a short screw going through the circuit board and screwed into the socket. The screw was only about as long as the thickness of the plywood so I countersunk the screw holes with a Forstner bit.
As for the length, well, if I’d glued in the bottom piece of the two-piece nose cone, I would’ve had a problem: the altimeter extends just about to the top of the body tube. But as it is, the bottomless nose cone goes on fine, leaving the altimeter fitting snugly but completely within the payload space. Almost like I planned it that way.