Today I finally got to test fire and function check my new AR9 build. No body died.

Long story short, it's not resetting the trigger.  Seems like the BCG isn't going back quite far enough to reset the trigger, even though it's catching the new round and feeding/extracting/ejecting just fine.

So, do I try a lighter buffer?  a lighter spring? a different trigger?


NFA 80% LRBHO Lower
NFA Stripped LRBHO Side-charging Upper
Geissele SSA-E Trigger
KVP 7.5 oz Buffer and AR9 buffer tube kit with KVP Extra Power 17-4 SS PCC Spring under magpul fixed moe carbine stock
KVP 16" barrel under carbon fiber tube
KVP BCG 9mm

Rounds are X-Treme 135 RNFP bullets over 3.4g Titegroup, and are my standard pistol load.   In spite of it being a single shot at the moment, managed to get it sighted in with a new Vortex Venom 6moa RDS and was hitting steel at will at 100y.

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UPDATE
Got back out to the range today.  No bueno.  Still not cocking the hammer on the SSA-E (or the SSA **see below)

Tried:
7oz KVP buffer w/KVP hi power spring
7oz KVP buffer w/standard carbine spring
7oz KVP buffer w/spare standard carbine spring
7oz KVP buffer w/AR-Pistol spring
7oz KVP buffer w/larue white carbine spring
7oz KVP buffer w/larue red hi power carbine spring

Then I tried it with the standard carbine spring & a standard 3oz
carbine buffer, still no dice.....which was really surprising.  Going
with the assumption that the hammer wasn't resetting because the BCG
wasn't going back quite to the end of it's run where the hammer resets,
that it needed a lighter spring or lighter buffer.  When I tried BOTH,
and it still didn't reset, I was...surprised.

But then since I didn't have any other spring options with me anyway, I decided to try
making the KVP BCG lighter by driving out the roll pin and taking out
the buffer weight, making it weigh only XXXXXX, but that did not help my
build at all.  Still a single shooter.   My friend's nearly identical
build (same upper & lower receivers, same brake, barrel, buffer,
buffer spring, stock, same LPK...different trigger, grips, handguards.)  
His PCC started cycling at this point, about 8-9 out of every 10...but
still not resetting on some.   He had a Timney AR trigger. 

At this point, without the weight in the BCG, and with the lightest spring
and / or buffer...if it's not running, it's gotta be the trigger.

So I swapped the SSA-E for the (nearly identical hammer ergos on the) SSA*** and tried that -- same result -- a single shot.

Next up -- gonna pull a 6 pound trigger out of another build that has much
closer to mil spec hammer ergos, and try that....or - buy a hyperfire



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UPDATE #2


I switched to a Hiperfire 24C trigger and it's now running like a sewing machine

not sure on your trigger, spring could be backwards.

I will say, you should be able to hit steal at 300 with a red dot.  I can with mine, i hit 7/10 at 400 with a $75 scope.  basically lobbing 9 mm bullets

Try lighter buffer

Like a 5oz?  And I only have 3oz buffers around in my other builds

You think it's the trigger?  Based on internet talk, I was under the impression that SSA-E's were good to go.  But this could also be the problem

If you slap the trigger does it reset? I had a Geissele Hi-speed in my 16" PSA (stock buffer and spring) and it would not reset unless I slapped the trigger. Swapped it for a Timney in my 5.56 and the Timney reset every time.

I should have mentioned in the OP, the bolt IS locking back on empty mags.....in spite of not resetting the trigger.

I'm using the spring that came with the buffer 'kit'...it's a KVP Extra Power 17-4 SS PCC Spring

I've got no chrono data on my loads.

I'll have to try that and see....

Meanwhile, I've heard that most Timneys are GTG....but I don't have any Timney AR triggers

I'd put a GI trigger in before spending any $$$

everyones got one laying around.

You could look at the trigger thread I started to find one that does work.

Also...verify you are not dragging the bolt on the ejector.



.

I literally don't.  Every AR I've ever bought had an upgraded trigger, and everyone I've ever built had an LPK that had no FCG, because the triggers were going to be upgraded anyway.

Yeah - I read your thread before I created this one.  It doesn't solve my problem.  Because their is guy there who says he also runs a KVP bolt and has no problems with a SSA-E

At this point I'm pretty sure if I change my high power carbine spring to a standard carbine spring, it'll run like a 10-round sewing machine.  I will report back

My SSA would not reset in a DDLES lower with a Glock'd bolt.

Swapped a gritty PSA FCG for the Geissle two stage and it'll reset every time.

Bolt/FCG pairs need to be tested.....

just wondering, is this something unique to Glock AR 9mm set-ups?  or applicable to Colt-style also?

i usually use an SSA-E in my AR's, but went straight to the BFS3 for my Colt-style 9mm AR, which BTW is now working fine.

I have that same bolt/trigger combo and it works fine. My only guess is the bolt travel is a bit shorter than with mine (I'm running a KAK 9mm buffer). Maybe try a regular carbine buffer with quarters as spacers, adding one at a time until it quits. Then you know how much bolt travel you need and can trim your 9mm buffer bumper accordingly.

FWIW...

The Rise Armament RA140 works great in my NFA glock lower with NFA  bolt.

Worse trigger evar when used in Palmetto State Defense Colt lower with Spinta bolt.

So it is sorta hit or miss some of the time with these damn things !! Especially for me since I build all my stuff using 80% lowers...just that much more crap to worry about.

Thankfully, the recent price-drops are making a wider range of good triggers more affordable.


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UPDATE
Got back out to the range today.  No bueno.  Still not cocking the hammer on the SSA-E

Tried:
7oz KVP buffer w/KVP hi power spring
7oz KVP buffer w/standard carbine spring
7oz KVP buffer w/spare standard carbine spring
7oz KVP buffer w/AR-Pistol spring
7oz KVP buffer w/larue white carbine spring
7oz KVP buffer w/larue red hi power carbine spring

Then I tried it with the standard carbine spring & a standard 3oz carbine buffer, still no dice.....which was really surprising.  Going with the assumption that the hammer wasn't resetting because the BCG wasn't going back quite to the end of it's run where the hammer resets, that it needed a lighter spring or lighter buffer.  When I tried BOTH, and it still didn't reset, I was...surprised.

But then since I didn't have any other spring options with me anyway, I decided to try making the KVP BCG lighter by driving out the roll pin and taking out the buffer weight, making it weigh only XXXXXX, but that did not help my build at all.  Still a single shooter.   My friend's nearly identical build (same upper & lower receivers, same brake, barrel, buffer, buffer spring, stock, same LPK...different trigger, grips, handguards.)   His PCC started cycling at this point, about 8-9 out of every 10...but still not resetting on some.   He had a Timney AR trigger. 

At this point, without the weight in the BCG, and with the lightest spring and / or buffer...if it's not running, it's gotta be the trigger.

So I swapped the SSA-E for the (nearly identical hammer ergos on the) SSA and tried that -- same result -- a single shot.

Next up -- gonna pull a 6 pound trigger out of another build that has much closer to mil spec hammer ergos, and try that....or - buy a hyperfire

Your problem is with hammer geometry to bottom of bolt...  you need to verify that hammer in the drop-in trigger assembly dupes that of a COLT factory M16 Hammer for height and radius at top of hammer face..

I switched to a Hiperfire 24C trigger, and it's now running like sewing machine

I ran into what sounds like the exact same issue using a Geiselle Super Dynamic 3 Gun trigger in a Colt pattern SBR.  The hammer just followed the bolt home when fired.  I contacted Geiselle.  They were great.  Actually sent me a second SD 3G trigger to try out.  Same result.  I then tried a Gieselle Super Dynamic Enhanced trigger and it ran flawlessly.  Also ran a GI and Hyperfire triggers without a single hitch.  There is just something a hair different with the geometry in the 9mm bolt and some types of triggers.  Somewhere on the Internet is a fairly comprehensive list of what triggers work and which don't with various 9mm bolts and pattern lowers.  I compared my results at the time with what they published and it matched up.  Would have saved me a ton of time an $s if I had found that first.  I'll try and track it down.  It's been years.

We have one going right here on ARF:

http://www.ar15.com/forums/t_3_15/713015_The-complete-9mm-AR-trigger-thread--What-works---what-doesn-t-work-database--Please-add-yours---.html

Different resource, but equally if not more helpful.  Thanks for pointing out!

I have found that the hammers on the SSA-E actually seem a little shorter than MIL-SPEC and do not seem to work properly with the 9mm bolts as well.

2 stage triggers are hit or miss in the 9mm builds. I've been running an ALG ACT with great results. These builds require some tinkering with triggers, buffer springs, buffers etc to get them just where you want.

I invite everyone to add their trigger/buffer/bolt set-ups in the trigger thread if they haven't done so yet.
Also post what combinations didn't work, and any other info you feel would be helpful.

Thanks.


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