WA M4 GBBR hammer bounce

[Johnser]

Hi all.

 

Hope someone can help. I have an issue with one of my G&P M4's. I'm getting hammer bounce. The rif is firing twice with every trigger pull. 

 

If I take the upper off and reset the hammer and pull the trigger I can see the hammer bounce when it fires rather and just hitting once. Any ideas on what part I need to replace?

[Nick G]

Sounds like the hammer spring if it's alowing the hammer to bounce. 

[Johnser]

Thanks for the reply. I've actually replaced the hammer spring and it's exactly the same. I know it's an odd analogy but it basically a little like when you put a ruler on the edge of a desk and twang it. Exactly like that. It's very odd. 

[JimFromHorsham]

In the most part it’s too much spring tension or preload  behind the hammer , the valve pushes the hammer back but there is still too much tension in the spring .

[Johnser]

I think I'll disassemble it and see where the issue is. Thanks for all the help and suggestions. Really appreciate it.