Was gonna say that too, its the same with anything locked, chained etc, little is going to stop someone actively prepared but thats a less likely senario, a basic level of security however may stop the casual Herbert whos just looking for some easy items to flog for a small reward which is usually what most break ins tend to be.
You'll Shoot your eye out Kid
Is this security chain to be used inside a secure premises, inside a securely locked cabinet of sorts to secure your airguns from unwanted removal ? Long gone when your airguns were ok under the bed or in the sock draw.
If the above security measures applies, a simply cheap but effective way could be curtain wire,with eyelets big enough for a quality padlock to fit, quality rather than size, passed through a larger eyelet stuck to the side of cabinet, Bostick' Sticks like S**t is brilliant, and that will secure your airguns from unauthorized removal. Unless the unwanted remover comes tooled up with bolt (wire cutters)cutters in which it won't make a lot of difference as your prized collection will be badly damaged while having unauthorized removal.
You can get stainless wire rope from a yacht chandlery.
They make them up to order and fit eyes on the end.
They can fit plastic coating to stop the sails from chafing on the stays.
Repariere nicht, was nicht kaputtist.
I bought an air arms prosport new and it came with a security chain not had one with other makers