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AR9 going full auto


aandabooks

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Picked up a PSA AR9 and immediately did a bunch of upgrades including a 3lb Velocity trigger. Got out to shoot the rifle for the first time tonight. Started well for the first few rounds loaded 1 and 2 in the mag. Loaded up a full mag and about 7 or so rounds in the gun went full auto. Ruptured cases getting thrown out and a couple times the mag got blown out of magwell.

I was shooting reloads that I run through my XDm at 132PF. Got home and pulled out the Velocity trigger. Started inspecting and everything seems to be functioning properly. Put in a Timney that I have in my AR15 and will be heading out for testing tomorrow.

The AR9 has a PSA hybrid bolt in it. Is there a modification that needs to be made to properly run an aftermarket trigger in an AR9?

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9mm AR15s blow a lot of crap back into the lower receiver. This crap can cause trigger contact surfaces to drag/stick, potentially causing what you are seeing. I have had similar problems with Timneys too. I suggest you try a regular GI trigger and see if it solves the problem.

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Is that the same Velocity trigger that says on the website in big red letters not for use in 9mm conversions?

There are a few things working against you here. Typically for a blowback 9mm you want to stick with something utilizing GI style trigger geometry and a relatively heavy spring on the hammer. Also as noted the blowback guns are really, really dirty.

The ruptured cases suggest to me that the hammer isn't helping delay the bolt's rearward travel long enough for pressure to subside before the case starts to extract. If you look at the JP blowback 9mm they use an adjustable trigger with their speed hammer (premium parts with optimized GI style geometry) and the heavier spring set that they offer.

Even if you could up the spring rate, or use a heavy enough buffer to keep the cases together blowback ARs are hard on hammer pins and trigger components.

If I were running a blowback 9mm it would get the either an ALG ACT trigger (or the BCM or PSA equivalent), a JP with the heavier springs if you need the shorter pull and reset, or work over a stock trigger to limit pre and over travel.

I honestly don't think even a GI trigger will present a problem at USPSA distances using a PCC. That wouldn't stop me from trying to improve the pull, but I would shoot for one of the setups I mentioned above.

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I run a blow back AR9 with a CMMG ramped bolt and a Timney trigger. I do run it with anti- walk pins but have had zero issues so far. I have about 1500 rounds on it so far and have let it go as far as 800 rds without cleaning it. I'm running 126pf loads in it with a wolf extra power buffer spring and Spikes ST-9x buffer.

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Put the Timney from my AR15 in the AR9 and ran 125 flawless rounds through it. 100 WWB and 25 of the reloads that I used the night before. I'll have to make sure I keep up with regular cleanings.

Mike, not sure about the warning on the Velocity. I bought it off an Ebay seller. Guess I should have done some more research. Now I'll have to take the AR15 out and test it with the Velocity trigger.

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Put the Timney from my AR15 in the AR9 and ran 125 flawless rounds through it. 100 WWB and 25 of the reloads that I used the night before. I'll have to make sure I keep up with regular cleanings.

Mike, not sure about the warning on the Velocity. I bought it off an Ebay seller. Guess I should have done some more research. Now I'll have to take the AR15 out and test it with the Velocity trigger.

I would anticipate you'll like the velocity trigger in the AR. I have one and it's worked fine.

9mm ARs can be a bit finicky about trigger group and bolt set-ups.

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