Aight y'all. Budget under $800, do I go with a Just Right Carbine or an AR15 platform 9mm? Usage will be USPSA and Steel Challenge matches. Will see 500-1000 rounds per month. AR would be a PSA upper and lower.

Out of those two options I would pick the CX4 Storm.

Owning both the Just Right Carbine and the CX4 Storm and having owned two 9mm AR's I find this a intriguing question. First of all, I love the light weight and fast and accurate performance of my Storm. I love the dependability, smooth shooting, and accuracy of my JRC.  Both of these are more accuate than either of my 9mm AR's. Others may have different experiences with theirs. For me personally based on my own experience I would pick the JRC over the 9mm AR, but again, that is just based on my experiences.  
BTW, both of my 9mm AR's used Rock River barrels, one with a RR bolt and mag well conversion the other a CMMG lower with a CMMG ramped bolt. The CMMG was a bit more reliable but neither was too troublesome .

I haven't seen or held one locally for a couple years now. I had not thought of that option yet. Thanks.

forever4.........are the JRC barrels threaded ????

Mine is and I believe all are now.

re:accuracy... my AR9 will cloverleaf 3 shots at 25yd....handload Bayou 135s and SPARC II... basically what you quoted for an AR9... NFA lower and bolt with a PSA 16" upper... I did have to ream the throat to get the 135s to extract live

Let's think about this for a minute....

AR9 shares most of the same parts that are interchangeable with the 5.56 AR platform.

This includes anything/everything you need to go faster, and shoot better.
These parts are getting better/cheaper/lighter  every week.

Now how many parts interchange on Berettas and JRC's ??
If something breaks or wears on those, can't get a replacement part very easily....or cheaply.

Next...try to clean a JR carbine, or a Beretta CX
Then...let's talk weight.


Personally, the only real decision that you have is Glock mag lower, or Colt mag lower for your AR9 build.


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Those things said....I have owned two 9mm AR's. While both worked well  neither would shoot as accurate as my JRC or CX-4.   Now, the CX-4 trigger needed some attention and it took all of five or ten minutes to make it much better than stock. But, it will never be as good as a good AR trigger. The trade off is you get a highly reliable, accurate firearm that will last a long, long time.

The JRC is a very dependable firearm. It uses AR FCG parts and can have a very nice trigger. It is a bit heaver than the AR9 but the payback is that mine will shoot rings around either of the two 9mm AR's I had (Rock River and CMMG parts).  I sold both my 9mm AR's and have never missed them.

But everyone is different and what is good for you may not be good for me.  As they say, YMMV.

It's a little above your budget, but my 10.5"  Rock River LAR-9 will shoot 1.5" to 2" five shot groups at 100 yards with hand loaded 125 gr XTP or 125 gr HAP bullets.  Back that up to 50 yards and you've got 3/4" to 1" groups, and at 25 yards it's a one hole group.  I suspect it will do that with pretty much any quality jacketed bullet.  Even with low cost 124 gr and 147 gr plated bullets, I'm getting 5 shot groups around 4" (6" with the 124s) at 100 yards, and it'll do it all day long cold barrel or hot.

I also like Rock River's modified Colt pattern design and the ability to use RRA, Colt, Metalform or modified Uzi magazines.  Surplus German and Israeli Uzi magazines are still pretty cheap with excellent condition magazines selling for around $10-$12.  They are also incredibly durable.

I've had exactly one malfunction with my LAR-9 and that was ammo related.  Cast bullets, FMJs hollow points - it isn't picky.


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I can't speak for other AR-9s but it is certainly possible for a well made AR-9 with a decent barrel to deliver very good accuracy.   And or course, you get all the ability to customize the configuration of the rifle that you'd get with any other AR.  


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My caution on 9mm ARs is that you do have to pay some attention to how you mix and match the parts if you build one.  The bolt is just that - a solid bolt, no bolt and bolt carrier and it's a blow back design that requires a heavier 9mm buffer, and a compatible buffer tube and/or spacer to run right.  The specific bolt carrier design (ramped or not) also determines the hammer profile that will work, with non ramped bolts normally requiring non notched or full auto hammers.