Here's the MVB ARC stock referred to above. You can see the deployment button on the right side of the machined aluminium Butt-Plate. This is a very high quality stock which locks up tight both extended and collapsed. It uses a standard BCG, which means that it will work with most piston guns and pistol calibre BCGs. The biggest down-side of this stock (besides the price!) is the short length of pull. It is similar to the CCS and Troy stocks in that it is definitely shorter than the standard Carbine stock. As a result, the MVB ARC stock is best suited to use with irons or short eye-relief optics.
Here's the LWRCI UCIW Ultra-Compact Carbine Stock installed on a 9mm carbine. It is actually quite short in the collapsed mode, but mimics the length of pull of a standard AR collapsing stock when extended. It uses a proprietary (shorter) Buffer Tube, with a flat-wire Spring and shortened Carbine Buffer. Otherwise, it uses a standard BCG and operating system. If you wish to run a pistol-calibre blow-back BCG, you will require a special heavy short Buffer from "Heavybuffers.com" (yes, they ship to Canada). I don't have an example of LWRCI's PDW Stock, so I can't comment other than to note that it uses a proprietary BCG and therefore won't work with piston guns or pistol calibre conversions, whereas the Ultra-Compact Carbine Stock will work with both.
I also own one of the NEA CCS units and have handled the Troy PDW stock at SHOT Show. Both are essentially the same, although the Troy version is machined and finished to a much higher standard. Both use a proprietary BCG with an integrated buffer in order to reduce the Buffer Tube to the shortest possible length. Both suffer from the same shortcomings - an overly-short length of pull and incompatibility with piston guns or pistol calibre conversions. The MVB ARC shares the short length of pull, but at least it functions with piston guns and pistol BCGs.
Finally, here is one of the new crop of PDW stocks that made its debut at this year's SHOT Show. PDW stocks were a definite trend at SHOT 2016, with new examples from several manufacturers such as Battle Arms Development, Maxim Defense and others. I managed to pick up a "dealer sample" of the Maxim Defense stock on the last day of the show for a reduced price of $300 USD. The MSRP will be $450 USD, putting it firmly in MVB ARC and Troy territory cost-wise. The key difference with the Maxim stock is that it ships with a custom-length JP Silent Capture Operating Spring, which typically sells for $140 USD when sold separately. As a result of the JP Spring design, this PDW stock system is not compatible with proprietary BCGs such as Primary Weapon Systems (PWS) or pistol calibre conversions. Now the good news - at the expense of a slightly longer buffer tube than the NEA/Troy/LWRCI PDW stocks, the Maxim Defense system uses any standard BCG just like the MVB ARC stock. The difference is that the Maxim Defense stock extends to the full length of a standard carbine stock, giving a standard length-of-pull. Instead of being all scrunched up against the rear sight/optic, there is plenty of room for taller/bigger statured users. Hallelujah!! Finally, a PDW stock with a full length of pull! That alone, almost makes it worth the price of admission. The Maxim Defense stock is very nicely machined and finished - on par with the MVB ARC OR Troy PDW stocks. It should be noted however, that the Maxim stock is a bit "rattly", whereas the others all lock up tight. It is not weak or flimsy, the Maxim stock just has slightly looser tolerances.
Hopefully the above helps shed some light on the various PDW stocks out there and their relative strenths and weaknesses. While my experience with these stocks is by no means complete, I have either owned or handled just about all of them at this point. My money is on the MVB ARC where a shorter eye relief will suffice, and on the Maxim Defense stock if a longer (eg. standard) length-of-pull is required. That said, the Battle Arms Development (BAD) stock looked a and felt pretty good, incorporating a carbon fibre check-rest into their design. All of that to say that no matter which you select, YMMV....
Cheers,
It was to easy to see!
