I got my NN seated 1st time on my 521s (with Stan’s strips) but then had a nightmare every subsequent attempt. I couldn’t even get the bloody thing off one rim without resorting to cutting it off. A mate knocked up a ghetto inflator, and he also has a knack of being able to pull the sidewalls away from each other to allow the air to enter. We also found that 40psi in the inflator is not always enough, but he hasn’t failed when running 50psi
No such issues with SG Hans Dampfs. a pack pump does the job.