9mm AR trouble shooting

[craigkim]

I recently put together a 9mm AR pistol and, as I expected,.... I am having some issues with it.

My components are a Spikes 5.5" barrel, a JP bolt, a JP silent captured spring, and a Geissele rapid fire trigger. The lower is a CODA 9mm dedicated lower which uses Glock mags.

Anyhow, the issues aren't anything I have ever experienced before. If I fire it relatively quickly it will cycle and chamber another round, return to battery even, but will not reset the hammer. SO the hammer isn't "cocked". I find this to be strange because it is still cycling the ammo. I contacted JP and they said it is a trigger issue. I think it would be hard to find a more reputable trigger than Geissele, but maybe it is something simple.? I haven't contacted Geissele yet, but does anyone have any ideas how this is happening? I have previously used this trigger without issue in a 5.56 lower.

I know it is not ammo related, as it occurred with coated lead subsonics, 124 grain round nose, and Speer 147 grain defense loads alike.

 

[rvb]

bolt doesn't have to cycle as far to pick up a round as it does w/ a .223. I'm not familiar w/ the jp bolt, but depending on the ramp it could be that the bolt just isn't cycling enough for the hammer to catch. I would go through the motion by hand..... dummy ammo is best, or just ensure chamber empty/closed, put a mag in, dryfire and hold trigger, and cycle bolt just enough to catch the top round in the mag and release, then see if hammer remains back.

just a thought, first one that came to mind. Needing a lighter buffer/spring could be the cure to get more travel out of bolt (or hotter ammo)...

-rvb

 

[praff]

In a rifle caliber AR you would just put one round in the mag, shoot it, and if the bolt locked back you would know you aren’t short stroking or under gassed. You cant rely on that method with a pistol caliber blowback rifle. One reason is a lot of last round hold open’s aren’t reliable in a pistol caliber or they dont have one at all.

Put a standard carbine buffer and spring in it to see if the hammer resets. That combo is essentially too light of buffer and too weak of a spring for a 9mm. It should at least identify if short stroking is the issue. It wont short stroke with that combo (that is unless the carrier is hanging up on something else)

 

[NyleRN]

You have a lot of unorthodox components in that build. JP is more likely correct. Most G triggers will not work in 9mm ARs. Depending on how the bcg is cut, they can work but rarely. 9mm ARs need a full profile hammer. Put a mil spec trigger in it and see if the problem goes away. I'll bet you a pmag it does

 

[AngryRooster]

You have a lot of unorthodox components in that build. JP is more likely correct. Most G triggers will not work in 9mm ARs. Depending on how the bcg is cut, they can work but rarely. 9mm ARs need a full profile hammer. Put a mil spec trigger in it and see if the problem goes away. I'll bet you a pmag it does

In addition, make sure it's a round profile hammer, not a notched hammer.

 

[GNRPowdeR]

I had this issue with an AR9 build and the notched hammer was the culprit. Changed for a radiused hammer and everything worked correctly.

No experience with the G triggers, so I'm not sure about the chances of this being a contributing factor.

 

[craigkim]

You have a lot of unorthodox components in that build. JP is more likely correct. Most G triggers will not work in 9mm ARs. Depending on how the bcg is cut, they can work but rarely. 9mm ARs need a full profile hammer. Put a mil spec trigger in it and see if the problem goes away. I'll bet you a pmag it does

I guess I didn't put a lot of thought or research into my build prior to my purchases, hence (unintentionally) I got some "unorthodox" components. I wanted something unique. It's got a Noveske KX3 muzzle device, or an Obsidian, on the muzzle tucked inside the 5" CODA carbon fiber hand guard. Somehow, the barrel is listed as 5.5", but I guess Spikes lists the full length of the barrel, because it is only 4" from the upper receiver? The upper is one of the Spikes dedicated 9mm uppers. The upper, lower, guard, mags, and barrel are cerakoted in combat grey. I have an aimpoint T2 red dot and a sig brace on it.

I thought I would be good using a quality matching brand bolt and buffer, but didn't think about the trigger. I have always preferred Geissele triggers and all of my ARs and Scar have them. I think I have a mil spec trigger or two laying around to try, as that explanation makes sense.

Thanks for the suggestions. I will post a pic once I figure it out.

 

[NyleRN]

I guess I didn't put a lot of thought or research into my build prior to my purchases, hence (unintentionally) I got some "unorthodox" components. I wanted something unique. It's got a Noveske KX3 muzzle device, or an Obsidian, on the muzzle tucked inside the 5" CODA carbon fiber hand guard. Somehow, the barrel is listed as 5.5", but I guess Spikes lists the full length of the barrel, because it is only 4" from the upper receiver? The upper is one of the Spikes dedicated 9mm uppers. The upper, lower, guard, mags, and barrel are cerakoted in combat grey. I have an aimpoint T2 red dot and a sig brace on it.

I thought I would be good using a quality matching brand bolt and buffer, but didn't think about the trigger. I have always preferred Geissele triggers and all of my ARs and Scar have them. I think I have a mil spec trigger or two laying around to try, as that explanation makes sense.

Thanks for the suggestions. I will post a pic once I figure it out.

No harm friend. I didn't mean to come off as harsh if I seemed to. There's a great thread on arfcom in pcc section of the ar15 subforum that guys list parts they've used for 9mm builds that works and what doesn't. When manufacturers list 9mm barrel lengths it includes the extension too. That's why it's only 4" out of the receiver. I like G triggers and have several myself and was disappointed when I read of so many having issues with them when I was building my ar9. AR9s can be very finicky and with all the new whiz bang components out there it's just a crap shoot at times if it'll work. I don't have any first hand experience with the JP buffer setup but read positive things about it being used in 5.56 rifles