I have 2 9MM rifles.

1st is a Colt mag style with CMMG lower, Matrix side charging upper, CMMG bolt and JP silent captured spring.

2nd is a Glock mag style with Spartan lower, Spartan side charging upper with LRBHO, JP Enhanced bolt and JP silent captured spring.

When I first built these I had Timney drop-in styles in both and they either failed to reset or I was having 3-5 round bursts. I read that drop-in triggers sometimes have issues in 9mm AR's so I removed them. I did a bunch of research and determined I might have better luck with the Geissele SSA, which I use in my .556 rifles. The Geissele SSA is definitely my preferred trigger. I have no desire to go to any other. I like the 2 stage and I like the break. I also need to mention I fire all my weapons, rifles and handguns, using the trigger reset. You'd be surprised how many people take their finger completely off the trigger between each shot.

My Geissele SSA triggers worked excellent the first few visits to the range. Then all of a sudden, I begin getting 3-5 round bursts again with both rifles! Unbelievable. I clean my rifles after every trip to the range. Some people say I am bump firing and other people say the mil spec profile is the only trigger that will work reliably in a 9MM AR.

This has really caused some serious frustration as I have spent a fair amount of $$ on all these triggers and this problems is so intermittent. Sometimes it happens after a few magazines and the last time it was my very first trigger pull of the day. BRAP! 3 round burst!!

I even took the ALG ACT trigger out of my dedicated 22lr AR and tried it in the Colt mag 9MM. This trigger seems to work perfect and it is very nice..... but..... it is NOT a Geissele SSA.

I REALLY want to keep the SSA triggers in these rifles but I need reliability and cannot have these multi round bursts at my shooting range. They kinda frown on it.

I contacted Geissele and they gave me the obligatory answer of "These were designed for a .556 AR.. etc. etc. I was happy they responded but it was the standard CYA answer. I was hoping they would tell me they are currently working on a great trigger for the 9MM AR platform. No such luck.

PLEASE... PLEASE... If anyone has had this problem and may have a solution please help. I will definitely go with the ALG ACT triggers in both if that's what it takes.

Another thing I was wondering. Could this be related to my silent captured spring assembly? These do require the center mass weight to be removed from the bolt.

I use RRA/Spinta bolts and haven't had any issues with a mil-spec profile hammers or hammers that are similar in profile to the RRA NM hammer.  Not all bolts have the same ramping, so YMMV.

Assuming all function checks pass, the best thing to do to isolate the problem is to shoot one round, hold trigger back, release trigger to reset and then repeat as needed to see if you get any bursting at all.  If you do, then you have a problem with the trigger (probably disconnector related).  If no bursts, then the problem is likely the shooter.  Too light a trigger + blowback recoil = bumpfiring.

Your best trigger options are pretty much worked over/lightened mil-spec style.  AR9s are not NM guns...

FPNI

...needed to be said.

I went through a bunch of triggers before I found a drop in trigger that works perfectly.  

I have:
Quarter Circle 10 lower
Quarter Circle 10 upper
Quarter Circle 10 bolt
Carbine buffer
RRA 9mm buffer
Rise Armament drop in trigger.

I test fired it this past weekend.  

Suppressed and Unsuppressed:
115 gr - passed
147 gr - passed
165 gr - passed

I used a Octane 45 and Form 1 titanium 8" with zmachineworx baffles.  Test fired 300 rounds in all.

I am very happy everything worked!