I have a PSA glock style 9mm AR, bought the upper and lower from PSA, threw in a KAK 9mm exteneded buffer and the thing has been flawless for me.  I know a lot of people had trouble with them but mine has been good.

Just got my ISIS 2 out of jail and ran it this weekend with Lawman 147 grains subs.  Was getting both failure to feed, would hangup in the chamber as well as 3-4 round bursts.  Put it down and here I am.

Any thoughts?  Heavier buffer still?

Edit: I was using an ETS 32 round mag that hasn't given me problems before.  Will try a factory glock mag this weekend.

What kind of mount are you using to attach the suppressor?

Try different ammo. It sounds like a short stroke issue and it's not resetting the hammer.

This is also common with some after market hammers when a ramped bolt won't reset it

Did you try shooting the gun with the Lawman ammo without the suppressor? If it works without the suppressor then I guessing you need a heavier buffer, a heavier spring, or both. Hard to imagine the symptoms you describe as being the result of too LITTLE pressure.

Curious because I also have a PSA AR9 that I've occasionally attached a SilencerCo Osprey 45 suppressor to.  The AR9 was stock at that time, I purchased it as a complete pistol upper sporting a 7.5 inch barrel, and mated it to a complete PSA AR9 lower. Eventually the Form 1 came through and I added a stock. Shortly after shooting the gun suppressed I noticed that the end of my extractor was gone. Gun still ran just fine without the extractor except that I couldn't get a live round out of the chamber. To clear it I had to shoot it. I figured that the suppressor had increased the pressure enough to shear off the end of the extractor.

I returned the bolt to PSA who sent me a replacement after a number of weeks. During that time I acquired and installed a Kaw Valley 7.5 ounce extended buffer. Gun has run just great for hundreds of rounds after this change BUT I have not tried it suppressed.

And now I'm a bit hesitant to do so unless I have a few replacement extractors on hand.

1/2-36 fixed barrel adapter.

So could the buffer potentially be too heavy with the subs?  Seems far fetched with a can attached.  But I don't know shit :)

I did not.  After 1 mag with it going into 3-4 round burst I just put it away.  Thought about that after the fact as well, will try this weekend.  

Lots of people have had the extractors break on this gun, it's a well known issue.  I probably need to check mine as I wouldn't be surprised if it's gone now...

Update. Took a 12 ounce buffer and Wolff xp carbine spring to get this thing running smoothly.

Glad to hear it. Sounded like an issue with excessive bolt speed and bolt bounce.

Didn't make sense that "too little bolt speed" was causing the gun to start firing bursts.