Threads are clean and run about the same length as far as the eye can see. I also followed the threads with my finger nails on both cap to see if there were any indifference's but none that i notice. Also the pic is without any battery in the device.
I suspect that where the thread ends, it doesn't have a good finishing cut. if you know what i'm trying to describe.
I notified the vendor and they are convinced that the cap is within "normal tolerance" if it fires and will settle with further use.
Can you try twisting back and fourth trying to work it all the way in? Maybe put some Vaseline or something on it?