9mm AR biuld

[JD Spanner]

So I built myself a Colt style 9mm AR using a Spikes Tactical Magwell adapter that has the last round hold open . Seems to cycle ok (Only fired 10 rounds so far ). But doesn't hold open on last round. Using ACS 10 round pistol mag.
Could it be my buffer spring is too heavy . I'm using a 308 spring with a 7.5oz buffer.

Thoughts ?
Thanks
Spanner

 

[JD Spanner]

Is there no 9mm AR experts out there ??

 

[Rebel Rouser]

OPEN

CLOSED

Colt has a propriety 9mm buffer. They are black in color. 2 pc mechanical buffer weighs 5.47 ounces.

 

[RUSTSPOT]

Take slowmo video see how far the bolt travels back. I use that to diagnose my ARs. Check for travel and bolt bounce.

 

[JD Spanner]

I'm using a Kaw Valley Precision 7.5oz pistol buffer and BCG.

 

[JD Spanner]

Good idea on the vid . I'll try that.

 

[call2arms]

I made a spacer that goes in the buffer tube so the bolt does not get a running start at the bolt hold open. Limits the bolt travel.

 

[Rebel Rouser]

Added more pictures.