That design has what is IMHO the best takedown system of any repeating shotgun ever designed (except perhaps for that of the Burgess police folding shotgun, on which the 520/620 were based). See
http://www.nramuseum.com/the-museum/...lding-gun.aspx if unfamiliar with the Burgess).
Don't forget that the 520/620 and their 'store brand' namesakes do not have disconnectors, and will therefore 'slam fire' like the Winchester Model 97 and Model 12, the older Ithaca Model 37s, etc. That means if you hold the trigger down and close the bolt on a live round, the gun will fire when the bolt locks. Remember your Four Rules always, but especially when handling a slam fire pumpgun.
lpl