Atoz / KA Dragunov: wild flyers?

[Trasher]

I've recently acquired an Atoz / KA / KM / Zastava spring Dragunov in "like new in box" condition. I think all the internals are stock, rifle chrono'd 460fps w/ .20. The hop unit is blue.

 

I get pretty consistent groups at 50 meters w/ .29 SGM when everything is working correctly. Problem is, I get strange "misfires" more and more frequently. When the "misfire" happens, BBs get extremely overhopped and the sound of the rifle is also different from normal. After 1-3 shots everything goes back to normal like nothing happened, normal hop, consistent hits, etc... Then .29s go vertical after 20-30 meters again.

 

Disassembled the rifle (since it will be upgraded to higher fps and hard hop rubber), but I see no damage on the parts.

 

I'd appreciate any tips, before I start experimenting.

 

Inner barrel horizontal play?

Nozzle play?

Bucking nub?

BBs hitting the outer barrel / flash hider?

[The Bushman]

I have never seen one, but I can suggest to eliminate the last option on your list (hitting flashhider) you could use a ramrod (from a loading rod). Insert the rod into the inner barrel and see if it's not aligned with the outer parts?

 

Must admit I'm abit confused, but my gut feeling is either BB's not seating properly or the spring mechanism that pushes down the hop spring is getting stuck and only occassionally dislodged by pellets passing?

 

...but that is clutching at straws and probably not the reason for your bizare and sporadic a problem.

 

Good Luck

[Trasher]

Thanks Bushman!

 

The internals are more simple than my VSR.

 

The piston is not fully encased, the tail end hangs out of the cylinder, engaged by a huge sear. Since the piston is not fully supported like on the VSR, I'll try to add a spacer ring to the piston body to avoid slight alignment problems.

 

Another different part is the cocking system. The nozzle/cylinder is never *locked* in the forward position like on a bolt action, only secured by a recoil/return spring and the friction of the hopup chamber. I tried different cocking methods (letting / not letting the bolt slam forward, etc), but I see no difference.

 

The inner barrel is shorter than the outer barrel, plus the long SVD flash hider. The inner bbl is centered by 2 O-rings.