It's all one solid piece, it was machined to look exactly the way it does.

there's some type of plastic stopper on the one end of it, and there's something that moves on the inside.

I'm not good on guessing the weight, but I'd say, maybe 1 pound.

Thanks in advance for your help!

you have a buffer from a ar 15 .16 type rifle or m-16 ect. don mack

What does it do?

Also, sorry if it's very obvious to everyone here as to what it is and what it does. I don't have any knowledge in this area of expertise.

The buffer cushions and slows the rearward thrust of the bolt and carrier assembly when the rifle is fired. It has a number of solid steel "slugs" inside that slide loosely back and forth, diverting the recoil forces. The nylon plug is to cushion the assembly from battering against the rear of the buffer tube.

The flat end, rests against the bolt carrier. The nylon end, is inserted inside the recoil spring. Spring and buffer are both inside the buffer tube, which is inside and supports the buttstock

OK. That's been answered, and quite well. Maybe this one should be closed?