I've been looking at the JR Carbines for the past couple hours... being I like weapons using similar magazines. Think it will be a future purchase. Maybe a tax return present.

Kind of narrowed it down to two options; .40 M&P magazines or .45 Glock magazines. Those are the only pistols I own that use those magazines.

With the .40 M&P magazines, I'm guessing that the Compact magazines will work in the JR Carbine, correct? Fifteen rounds of .40 is nice, but if need be, I rather be able to toss in the 10 rounders (have both a 5" Pro and a Compact).

I'm kind of leaning towards the .45, since I already own a 9mm Beretta CX4 (can use the magazines from my 92 Brigadier Inox or my PX4). Go big or go home, right? Anyways, I own a Glock 30S, which is my off-duty gun. I have a few 13 round magazines, but most of mine are 9 and 10 rounders. Will the smaller ones fit in the JR Carbine? I've looked on YouTube and via an internet search, but not any info that told me a definite yes/no. From seeing the videos of the 13 rounders in the gun, I'm feeling the same way as I do about the M&P magazines, but rather find out to start making a plan.

Thanks.

I can't verify this since I don't have any G30 mags for my JR .45 carbine but the g21s stick out below the bottom of the trigger guard enough that there should be plenty of clearance, i can't imagine why they wouldn't fit.

Thanks guys.

I went on YouTube and found a guy that was showing off issues with a .45... and he used the short 30 magazines as well as the larger ones (20somethingish).

Now, just got to find a .45 takedown with a non-threaded barrel and fixed stock. Something to look for at the next gunshow.

Early versions of the JRC in 45 ACP did have problems.  I know I owned one.  But Since I live near where they are built, I made several trips to them and they finally got it working.  They were great to deal with and offered my my choice of replacement carbine if I wanted one.  Being an old QA engineer I became fascinated with the problem and stuck it out.  

The main issue was a timing issue.  The carbine cycled too fast for the Glock magazines to keep up,  They finally got the carbine slowed down and I was able to get 500 rounds through it without any problems when NY passed the "SAFE" act.  So now it resides out of state.  I hope to be residing out of state soon too.

yes the smaller [ 10rd] mags will work . I have the 9mm version and all mags work, right up to the 33rd units.  They make a CA compliant unit.

Mine is the later .45 version with the heavier buffer, the mag mine came with did not have the modified spring and would not work reliably but the extra Glock factory13 rnd  mags I bought I had already done the JRC recommended spring mod (just bending the top loop upwards in the back) and they ran fine. So the spring mod is absolutely necessary to run at all, once I modded the factory mag it too ran OK.Since then I've tried the stock Glock mag springs, Wolff xtra power mag spring (heavier than the Glock springs) and the replacement JRC springs, which are stronger & longer than the Wolff springs. Doing the spring mod will lose one round of capacity but the modded JRC springs were the only ones that would feed 12 rounds reliably all the time. I also picked up an aftermarket 27 round mag and replaced the +2 baseplate with a flat plate to increase the spring tension, with the spring modded it seems to run about 18 rounds reliably. I think to get it to feed more than 18 it needs a heavier spring but haven't found one yet.