I'd like to get the binary trigger that will run with the least hassle in a 9mm  AR.

I've got a Mas Defense 4.5" upper with a Spinta bolt.
Right now I've got a carbine spring with the PSA 9mm bolt and it runs fine with steel and brass ammo.

The videos I've seen make it look like the Echo will run if the bolt is milled out.
(Not crazy about this option.)
Some of the videos of the BFSIII look good, but some people report they can outrun the bolt if they try.

Any input appreciated.

Looking on Spinta's site and knowing what the PSA bolt looks like, I don't think either of your bolts are compatible with the Echo AR II.  I ended up purchasing the American Resistance Gear bolt/buffer/spring kit...it included a 4.7 oz buffer and DPMS .308 spring.

Call Spinta, NFA, FTM. CMMG, QC10.....etc, etc

Ask them directly if their 9mm bolts work with that trigger.

This is the best and fastest way to find out what you want to know.

Then, report your findings back here for everyone else to read.

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