The first thing that has to be right is the atomizer's 510 pin. It needs to protrude slightly from the threaded area of the 510 connection ... If it don't, it will short out when you press the fire button ... see the photo below
The second thing to check is the connection between the atomizer's 510 connection and the pin in the top cap of the battery tube. When the atomizer is screwed onto the battery's top cap, it needs to make connection. The best way to insure connection is to adjust that pin in the top cap so when the atomizer is screwed on it tightly, there is just a very slight gap between the bottom of the atomizer and the top flat surface of the tubes top cap ... If you do this, you can be assured that there is now a good connection between the two.
And lastly, when everything is put together, insert the battery and tighten down the tube's bottom cap .... the bottom cap should now hold the battery tight up against the tubes top cap when the bottom cap is tightened down .... if not, you will need to adjust the pin in the tube's bottom cap so that it holds the battery tight up against the tubes top cap when tightened.
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BTW ... Here you can see that there is also a slight gap between the tube and the tubes bottom cap once the battery has been installed and the bottom cap tightened down ... having this slight gap insures that the battery is tight between both end caps .... no chance of it not making contact: