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Help me out with a new AR9 build issue?


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Hey 9MM is what, about .35 caliber?   I know its not .308 but  you guys are the only AR specific forum I visit so I figured it was my best hope of some helpful info.


This is my first pistol caliber AR and I have only shot a handful of them over the years.      Over the 4th PSA had a 9MM rifle kit for $399     Seemed like a reasonable thing to jump into.


So I got the thing,  put it together (seemed to go well enough)      Took it out today and had issues.


It seems to manually cycle and chamber a round fine, however pull the trigger and most of the time you just get a click.    Seem to be quite light on the primer strike but I did get a few to fire (maybe 4 out of 20?)


Using the mag I bought from PSA every round chambered failed to fire.    Using a IWI 9MM Tavor mag (which snapped right in) I got a few to go bang but mostly FTF.  (I cant imagin that the mag has anything to do with it, but )


tried a couple different types of ammo, not a disenable  difference


Just looking at the bolt it seems like the firing pin is free and has enough movement to do the job.   It does seem to not sit very proud of the bolt where the hammer strikes it.  The hammer is stopped far before the pin can bottom (and its spring loaded)


I ordered a Wolff extra power hammer spring.     What else should I look at?


The PSA kit is a nonramped bolt and uses a standard LPK.   It does come with a 9MM specific buffer and action spring.


I didn’t think about taking a pic of the light primer strikes.   I ran the FTF's through my handgun without issue so at this point I can’t show how they looked.



Edited by ironmonster
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^^^  Yep, buy it.  Or, send your carrier out to get ramped.  There's a couple places that do this service.  It's better for it over the long run to run a ramped carrier. Easier on hammer pins.  Run KNS Anti-rotation pins, too, for the support to the hammer pin.


Also, how do your magazines hold in the lower?  Standard AR mag catch?  If so, consider buying some surplus UZI mags and modifying them - I've posted the template somewhere on this board.  I have 10 of them, marked them, cut them up, and they run great. 


Ramped carrier pics below.





Edited by 98Z5V
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I got the KNS pins in there already.      I read about it being brutal on the hammer pin so I jumped for those from the get go.



I can ramp the bolt probably easier than change out the hammer if you think that is the ticket.    I found a couple of posts on ARF.com laying out how to machine the bolt.   I got a mill and it sounds like its no more than 15 minutes worth of work.

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  They would still probably take a beating because they have to be the same Hammer /Trigger geometry as a STD FCG, but they may be more forgiving , only way to find out , is to try one . 

 How is firing pin protrusion on the Bolt face . Also have you checked the Head space , 9MM still has to have proper HS . 


Edited by survivalshop
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I have not checked headspace, I can pull the barrel and check using your measurement and a pair of calipers. It was an assembled and test fired upper from PSA ( I know that means little, but it should have been checked at least

I ramped the bolt this morning, put a 5 deg ramp which ends up being like 1.250" long. A high speed endmill wouldn't touch it, I ended up hand grinding it with a dynafile, glassbeading it and then putting some birchwood Casey barrel brown on it (blue would have been better but it's what I had).

It's not perfect, but should do what I did it to do ;-)


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I thought maybe I could reach down in with the tail of some 8" calipers but because of the substantial bevel around the chamber I can't get an accurate measurement. I'd have to pull the barrel and don't have time at the moment. I come up with .137 but because of going through the upper it's not straight enough to accept that as the number. I am assuming that + .002 would likely be at the edge of no go range?


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I recently bought a PSA 9mm carrier to convert my Diamondback AR pistol to 9mm, while I did run into an occasional round that didn't chamber

most did and all those fired every time - the carrier is factory ramped from PSA, perhaps they sell both ramped and unramped varieties. I'm 

suspecting the chambering issues I'm having may be related to the Promag Adapter or the ASC mags that I am using  <dontknow>

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Anyone have issues with the mag catch being long enough to work through the adaptor block? Mine was not secure. It "kind of" worked but every once in a while a mag would simply fall out. On inspection only about a 32nd was catching.

I tig welded on a dab of inconel and polished it up. Big improvement.

Is this a typical issue?

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Personally, I'm not sure on that, brother - catch engagement on a mag adapter - just because I'm not running an adapter.  The 9mm lower is a dedicated lower from first-build, and on the AR45 it was "standard lower with Oly special mag," then I went dedicated lower on that one, too.  I have zero experience with the mag adapters.



You did ANOTHER badass awesome job on that mag catch, though...  :hethan:

Edited by 98Z5V
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