Hi everyone,
Just bought a rrd rdm 340 mast. When I put bottom into top the connection is tight enough to not let the air out of the top part. The ferrule is like a plunger on a syringe. The mast springs apart, just a couple of centimetres.
I gave it a good clean and with a bit of soapy water I can see the air slowly escaping from the join, as I rotate the bottom part around.
Was thinking of just sanding the ferrule a little bit to give a bit more space for the air go, but as it's the first time I've come across this, thought it might be best to ask.
Any thoughts?
Thank you very much.

No that is good! SV does the same. Jam it in and tape the join with the 2" wide cloth tape. never ever have a stuck mast due to the great seal.
I love it

But Yeah a trap for noobs if it springs apart before downhauling it's a recipe for breakage

Also, water does not enter mast with this design.

Thanks to all for stopping me from doing something stupid.
Unbelievable how finite the tolerances must be to make something like this. Cause the cap on the end does not overhang to make the seal, it is all carbon/glass/epoxy. Just unreal.

Sounds like simple air lock rather than a defect. With tight-fitting masts like the RRD RDM 340 mast, the ferrule can seal so well that trapped air makes the sections spring apart if you push them together quickly. Try assembling with a slow twisting motion to let the air escape and make sure everything is clean and dry. I wouldn't sand the ferrule unless it won't seat fully or becomes hard to separate after use, as removing material can create play later on.