Sabre defense A3.  Took the barrel out to let it cool and then could NOT get the barrel back in.  Noticed there was a pin sticking out on the left side of the receiver.  The pin has a bevel on it and was loose inside its hole.  Adjusted the pin to let the barrel assembly slide past but there's noting to hold the sucker in there!  Fell out when firing and had to search the ground to find it.

I'm trying to find a parts diagram but can't see that part in anything online.  Have no idea what the pin is even there for.  Maybe to stop the barrel plate from hitting the receiver?

Not my picture but you can see it below - it's the one that's almost touching the barrel to the left of the charging handle.




Also, the rail/scope mount is loose on my gun.  What do you suggest for locking the hex nuts down?

Thanks

Yeah, yeah, I know I need an optic.  Can't afford it !
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You're correct that the pin is a stop. Degrease it and then glue it in with red LocTite or your favorite epoxy. Tap it with a brass hammer to ensure it is fully seated.
Use red or green LocTite when you tighten your hex nuts using a wrench.

thanks !  Seems like the pin really doesn't serve a purpose.

It serves the same purpose that all AUG receiver barrel over travel alignment stops serve.

All AUG's have a barrel alignment guide. The A1, A2, SR, and M1 have it built into the receiver. The A3 has it as part of the rail.

It serves to properly align the lugs of the barrel with the trunnion AND the barrel lock. Otherwise there could be risk of a barrel not locked in position when the bolt is locked into the trunnion...

4mm hex and red loctite. Don't over tighten, you'll be going directly into aluminum - not a bushing.

Borat had posted a link in Bullpup. Good call. lol

Maleante - how do you suggest mounting that pin in there?  What kitbuilder said?

It's not even a snug fit.

There's nothing in the armorer manual regarding the pin in the rail. I'd try kitbuilders advice and failing that, call Steyr and explain your problem. If you're nice, they may send you a new top rail if you send yours in - if there are any left...
Steyr does have exceptional customer service. If there is a way to help, they'll take care of you.

FWIW, the spec on the bolts regarding loctite is to use loctite 648.

I called Steyr and they said that the pin can be held in with JB Weld or Loctite.  He said to use Loctite 242 or 243 on the bolts for the scope rail.