AR15 / M16 parts identification help

[halo696]

Picked up a bunch of old AR15 / M16 parts awhile ago. I just recently decided to go through them all. I have these things that appear to be bolt inserts but have no idea what they are for. Weight maybe? They appear to have pencil engraved serial numbers on the ends. Anyone know wth these are?

 

[Nsegg]

Can't help you here, but now I'm curious as well.

 

[hamburglar3]

I had one in my Colt ar9mm bolt. I think it is extra weight to hold the bolt closed longer.

 

[halo696]

I had one in my Colt ar9mm bolt. I think it is extra weight to hold the bolt closed longer.

Thanks! Now that makes better sense because there are .9mm hammers in the same parts hamper.

How about these? .9mm parts as well?

 

[Allsmiles]

Those almost look like some sort of bolt carrier key since 9mm is blow back operated. Maybe to keep the bolt straight and ride the charging handle? Just guessing here however.