Pros and cons please! And , what is it actually made of? Thanks!

In general, lightweight frames are mostly aluminum, with small amounts of other metals, like scandium, that make the frame harder/tougher.
They are lighter, thus kick more, and are easier to carry.
The finishes are pretty good, but if you start scrubbing/sanding and destroy the finish, the results can wind up looking like an old aluminum screen door frame.

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Science plus Art

Pros: lighter weight for carry
Cons: not quite as durable but still plenty strong. Being lighter, recoil might be a little higher.

What model are you referring to? "Alloy" generally refers to aluminum....

The stainless frames are much tougher, but much heavier as well. Which is why the alloy frames are so popular.

The downside to the allow frame is twofold. first, if they frame lugs that engage the barrel lugs aren't properly lubed AND you shoot a lot with hot ammo, the allow can wear.

Second, if you have a worn recoil spring, it's possible, although still unlikely, that the frame will crack around the slide stop hole.

Which is why it's recommend that you replace the recoil spring on any new to you 3rd Gen. As was mentioned in your 457 thread, Springco Tactical makes a very nice replacement set of recoil springs for the 457/4513. It's cheap insurance.

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Can open, worms everywhere.

For extended carrying - Alloy.
For extended shooting - Steel.

Light weight is about the only real advantage. It wont rust but under the right condition aluminum will corrode.
Gary

Thanks guys, yes I will replace that recoil spring as suggested on my 457!