Anybody got any first hand info on this set up. Got a chance to buy one new $500 for a 45 acp using Glock 21 mags go or no go?

Run - buy it NOW! Average retail around here is $700 or so. I just got a deal on a used one with 3 Glock 33 rd mags for $575.

Shot one a few years back...still grinning. The controls are not identical to an AR though. I consider it its own platform. A fun one!

I have one in 9mm and desert digital pattern.  Runs well enough.  I have been thinking about SBRing it, but haven't quite committed to that yet.  As has been previously noted, it is a completely different platform (think Kel-Tec SU-16).  For that price, I would be on it like Rosie O'Donnell on a jelly doughnut.

I have one in 45, I would buy it again....

That's a great price, mine is very accurate especially with 185 gr. ammo.

Be aware, mine always ran fine with the factory JRC mag but with factory Glock mags I had to replace the springs with JRC's springs. Wolff springs weren't strong enough.

Also, the spring mod that's described in the owner's manual wasn't done on my factory mag, it didn't run right til I did that. It's simple, just bending the last half loop of wire up to put more pressure on the rear of the follower. You'll probably lose a round of capacity when you do this mod.  

I've gotten a hi cap .45 mag to run as well, started with an SGM mag which is just one of the Korean mags with a stronger spring. but that wouldn't run a full capacity. Removed the extended floor plate and replaced with a regular floor plate which would run about 20 rounds reliably but still wouldn't run at full capacity. Finally swapped in a Kriss spring, it was so strong that with the flat floor plate it had so much tension it would force the last round thru the feed lips, had to go back to the +2 extension but it works.

So you get this deal?
 I run factory 13rd mags with no issue. Tried the Kriss mag extension, on my carbine nothing but trouble. The weight of a full mag,combined with the length had it moving around, causing numerous FTF's.
Yet a 33 rd 9mm mag (both Glock and import) works fine on the spouses jrc 9 carbine.

Picked it up yesterday will try and get to the range today with range report to follow.

I bought the 9mm version a few weeks ago, but have yet to get it out to the range.  They look cool.

First, on your used one, look to see if it has a feed ramp/magazine stop. They made some changes on them over the years to make them run more reliably. I have the "late model" 9mm that came out a year or two ago and its nothing but sweet and stone reliable. It is also very accurate. On the 45 model check their website for some of the changes they have made to make them run better.

I posted about a cheap trigger job on this rifle in another forum. My stock trigger pull was like 8 pounds. I bought a Wolf trigger (not hammer) spring kit for about $6 and installed it. (Ten minute job). Trigger is now about 5 pounds and feels far better. Sweet shooing rifle made even better on the cheap!  

Love my JRC.

I dropped the QMS-ALG triggers in the ones we have.  While the upper & lower receivers are proprietary, it's nice one can use AR H/T/S & furniture on them.  

I got a JR carbine in 45acp a couple of months ago. I really enjoy it. With a red dot on top I can pop the 6" plates on a dueling tree at 25 yrds with out fail. Kriss  and SMG high cap mags were a failure for me. Glock mags w/JR springs are reliable 24/7. Reg glock mags  work well most of time for me. Over all it is a great carbine I would highly recommend it to anyone. Esp if they already have  a Glock.

Finally got out and shot my Jr carbine. This gun is great 150 rounds not a single malfunction of any kind. After zeroing it I was able to keep 13 rounds in about 2 inches at fifty yards with a red dot sight. Where as this gun been hideing all this time. Does anybody know if a standard barrel but and delta ring will work on this upper.  I do not really care for the quad rail want to swap it out with a magpul hand guard and stock. Barrel measures 750 so a clamp on front rail gas block should work.

Yes, they utilize standard AR furniture. I have a 13" strike ind keymod on the 45

Those of us who have the "later model" ones have been mentioning them a lot. Some just wouldn't adopt them because they weren't a "real" AR. After getting my JRC I sold both my 9mm AR's as the JRC would out shoot them, was stone reliable and used common Glock Mags. Not only that but its a simple and inexpensive operation to change calibers on one. A great piece, I love mine.

Not as good as I thought after about the first box started getting bolt over jams some are so bad the side of the case is ripped all the way open. Jr carbines are only open Monday thru Thursday that is shitty customer service right there. The one I have is supposed to be the latess and greatness. I HATE HAVING TO SEND A NEW GUN BACK TO GET IT LIKE IT SHOULD BEEN TO START WITH. We shall see.
  Tried all of the spring mods I found on the internet, still no joy.

The JRC is a good design. It would appear you have something wrong of course. Think about how well it worked at first, what changed?  Is it clean? Oiled properly? Different ammo? Different magazine?  There is a lot of information out there on these rifles. Some have had to tweak the .45 models a little, mostly due to magazines and some changes to the buffer or spring. Read up on this a little and think it through. The design of these rifles is solid, but like any firearm you sometimes have to learn more about what you have and how to make it hum.

The only thing that changed is the day and a different time. Used the same mags and the same ammo federal and winchester white box, even tried some known good reloads.. Got two to three jams with all four mags that I have.

Talked with Tony and come to find out my gun has the wrong buffer in it. 30 minutes after the call got a email new buffer is shipped and on its way. He said this should do it. Pretty good customer support so far. We will see I have a lot of plans for this carbine if we can get it running right.