NONE of the 57's were designed for civys.......you have the tactical with fixed sights and no magazine safety which is still deptment only and the Tactical Individual officers model(IOR) which has adjustable sights and a magazine safety(will not fire with mag removed) so there are two versions of the 20 round mag......the IOR version has a little shelf that pushes up on the mag safety to disable it so the gun will fire...the department only tactical will take either version mag
and so will the IOR, it just wont fire with the mag without the shelf. There are NO other differences between the two models and you could remove the magazine safety on the IOM and it would work with either version of the 20 round magazine. just be sure when ordering the hi caps to say its for a IOM model if your pistol is unmodified. a photo of the IOM 20 with shelf(the same shelf thats on your 10 rounders.
the fact that the IOM exsists at all is really because of the BATF importation rules and about whether something has sporting purpose or not.....the 57 could never be sold to anyone besides govenrment agencies(not individual officers or general public) until two things happened...a round of ammo that by its construction was not intended as AP(didnt have the steel insert) and a ten round magazine had to be created just for the U.S. market. Now that left the pistol itself being modified to show it had sporting purpose.....put adjustable sights on it and add a magazine safety as an afterthought...WAAALAAA! it has sporting purpose! Glock had to put adj sights on every glock to import and then change them out to fixed in smyrna Ga. back when they first was imported. So the IOM can be sold under U.S. law to anyone that can own a pistol
though a fixed sight tactical isnt illegal if you found one for sale on gunbroker.com...its importation is/was restricted for agency sale. I hope that makes sense....
there are several models now of the 57
1.the Five Seven = DAO/fixed sights/agency only(remember its not sporting purpose)
2. Five Seven tactical = single action/fixed sights/agency only
3 Five seven Tactical IOM = single action/ADJUSTABLE sights/mag safety added/anyone can buy though FN still only wants them to be sold to police officers only.
4.Five Seven USG(U.S.Gov't model)= Angency only, same as #2 but has a smaller more conventional trigger guard(the regular trigger guard is made to allow cold weather gloves,as it was designed for military operations. the USG is used by the U.S. Secret Service.