Sounds like an M14/M1A clip

 

Yes...it is a M-14 stripper. SEY stands for Seymour. I believe that there were a few font variations though out the manufacturing life of these strippers as well as a change(s) in spring design.
Mark

 

Awesome. My son will be glad to hear that. The 5 round magazine is a PITA to remove. He'll be able to reload it without removing it from the rifle.
I kinda figured of all the different types I have that this one would be one that I should have known.

While we are on the subject of stripper clips: I have some Argentine Mauser clips. Why do some have non magnetic bodies with steel springs while others have non magnetic springs and steel bodies. And have you guys ever seen them all magnetic or all non magnetic?

Motor

 

Standard "Nato Spec." 7,62 Cartridge clip. It has the same width as the US .30 Cal Springfield clip, but the Lug Position is to suit Nato Spec. Charger Guides (M14, FN-FAL/L1A1 Mag filler or Clip Guide; German G3 Mag Filler, Other Bolt rifles converted to 7,62 Nato.
Made of Blackened or Parkerised steel sheet. Israel made one compatible with both its FAL (with guides) and the 7,62 Mausers, and also the 7,9 Mauser (Marked 7,62-7,92)

Doc AV

 

Motor,
Collecting stripper clips can be a life time endeavor. I know a fellow who likes to collect the various manufacturers/variations of British Enfield strippers....he carries a little note book with the ones he has to gun shows and picks though boxes and bins of available strippers until he runs out of items or until he finds one he doesn't have. He's been doing it for over five years and will come up with a new one every so often.
As an example of your Argentine strippers.....there was probably more than one contractor and various subcontractors and various materials could have been used depending on what was called out during a production run. Designs may have changed or have gone through revisions depending on field use. Non metallic strippers or chrome plated were less prone to corroded as an example. It could also depend on raw material availability. The possibilities are endless.
But to answer your question, yes, I have seen and owned aluminum, brass, steel, plated, blued, parkerized and otherwise stripper clips with steel or other material that can be tempered to act as a spring.
One thing to remember, for the most part, strippers were meant to be disposable. They were carried in pouches or bandoleers and used for recharging the magazine and discarded. But they needed to be sturdy enough to be dependable when needed in battle or otherwise.
Happy to have identified you SEY clip.
Mark