Rear disassembly pin is wallking out on my Dlask Arms lower during shooting. The whole thing is almost new (something like 600 rnds). Whats wrong? Please help.

Sounds like the rear pin detent and/or spring is missing. If you push the pin out (like to open up the rifle) can you push it all the way out and remove it?

You mean completelly remove, to pull it out free? No, I cant. It stops when extracted for dissassy.

Detent? Sorry, what exactly is it?

OK, sounds like the detent and pin are in place. In that case it sounds like the takedown pin itself may be the problem. There is a groove in the rear of the pin where the detent is, and there is a small "hole" or depression on each end of the groove where the detent is supposed to drop in with a pronounced "click" to hold it either in the open or closed position. It sounds to me like the hole that the detent is supposed to drop into to hold it in the closed position is either not there at all, or is located wrong. Easiest fix would be to replace the takedown pin. Another possibility is the hole in the lower receiver that the detent and spring are  in could be located incorrectly. In that case you can modify the takedown pin with a Dremel (and a really tiny burr bit) to compensate, or have the manufacturer of the lower receiver correct the problem (most likely by replacing it).

Hope this helps...or even makes sense.

ETA: After thinking for another second or two, it's still possible that the detent is missing but the spring is still there and keeping the takedown pin from coming all the way out.  First thing to do is verify the detent is present.

OK, I thought it is this little piece. I hear clicking sounds on both stops, but I would have to check. It si a long way to go to Canada from here, so I better check myself first. Any safe way of dissassembling it?

Very easy!!  Simply remove the buttstock (remove screw #6 in Tweak's pic above) and the spring should be obvious since the buttstock holds it captive. Remove the spring and the detent should come out. If no detent comes out, see if you can then remove the takedown pin. Once the takedown pin is out you can push a small piece of wire through the hole and see it come out in the takedown pin hole (this will verify the lack of a detent). If the detent and spring are in fact present, it's possible that the wrong spring was installed causing insufficient pressure on the detent. It's also possible that the spring was pinched between the buttstock and the receiver when the stock was installed.

OK, I can see the problem. The buffer spring tube was loose and I was trying to tighten it. When I was playing with the proper position a little spring got in the way and was bent. i cut the bent part and reinstalled :-( But now I know what to check and how to fix it. Thank you very mcuh, guys!

OK, I will try it. Or get replacement part. Thank you.

Detent present!!! :-) I shouldnt have played with the thing, but the buffer tube was loose (telescopic stock)... I checked the thing and the spring for the buffer stop is a little bent (yes, I am a very good armorer ), but looks like it works fine, there was not a problem during shooting. Should I fix it or I shouldnt repair what is not borken? And I think I can get spare parts where I got the rifle. Thank you for all the advices!

Quoted: Rear disassembly pin is wallking out

Well, maybe if you had treated it nicer it wouldn't be leaving

Quoted: Detent present!!! :-) I shouldnt have played with the thing, but the buffer tube was loose (telescopic stock)... I checked the thing and the spring for the buffer stop is a little bent (yes, I am a very good armorer ), but looks like it works fine, there was not a problem during shooting. Should I fix it or I shouldnt repair what is not borken? And I think I can get spare parts where I got the rifle. Thank you for all the advices!

Hey, look at it this way - as a result of "playing" with it, you have gained useful knowledge of how the thing actually works.  Id' say that's worth the cost of a tiny little spring!!  Unless you were playing with it while under fire or something...

Manitou this wasnt very nice off you!!! h,Again, thanks for the good info.

The information button at the top of page would be a good place to start,
www.ar15.com/content/guides/

OK, lesson learned