Changing trigger for 9mm upper in AR??


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Orion8472
February 27, 2009, 12:28 PM
Why do I have to change out the trigger in my AR . . . if I want to use a 9mm upper? I have a very nice JP trigger in there, and don't want to mess with it.

Comments?

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KingTiger
February 27, 2009, 01:13 PM
Why should you have to change the trigger? Who told you that?

JDGray
February 27, 2009, 07:10 PM
You can use your 9mm lower with a .223 upper, but not vise versa. The 9mm upper needs a funky hammer due to the very heavy, odd ball bolt, and A .223 hammer may lock up on it. So I've been told.

nicholst55
February 27, 2009, 08:18 PM
Buy an Oly Arms 9mm upper, and you won't have to change a thing!

That said, some aftermarket triggers have displayed a tendency to fail to properly reset when used with some 'other-caliber' uppers. I know that some triggers will not reset when used with a dedicated .22 LR upper.

Walkalong
February 27, 2009, 09:17 PM
Some .223 triggers work fine. The DPMS style hammer will work with any set up. .223 upper. 9MM upper ramped or unramped. Some hammers need a ramped bolt. The RRA 2 stage for sure needs a ramped bolt. The RRA 9MM bolt has a little notch in it that the 2 stage can hang up in and lock things up.

First pic is my RRA 9MM AR with DPMS style hammer. Second pic shows the notch. Third pic is a professional ramp job. Fourth pic is my home done ramp job.

Ramping the bolt removes the notch as well as raising the point of contact of the hammer on the bolt reducing stress on the hammer pin.

Orion8472
February 28, 2009, 03:20 PM
Well, I don't want to do anything that will adversely affect my JP Enterprises trigger. The think is freakin` crisp, with a low lb. of pull. It is currently being used in a "long range" AR (.223) and to me, that's more important. Maybe I should look for another lower and then do a 9mm out of it. :uhoh:

Zach S
February 28, 2009, 04:57 PM
9mm is blowback operated, so its a little harder on the rifle. You may get doubles or bursts with a match trigger. I dont think its common, but has happened.

The unramped bolt is the biggest issue.

Due to the mag block and heavier buffer, another lower would be the best thing to do IMO, if you can find one.

xx7grant7x
February 28, 2009, 09:13 PM
I agree get an olympic arms upper, i've got one and they use sten mags and don't need replace parts. Mine shoots great with no hiccups yet

Orion8472
March 3, 2009, 04:36 PM
Thanks, guys. I may have to try that. My current AR is using an Oly lower that I bought FTF several years ago. Seems to be good stuff, as far as I can tell.

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