Just found this on gunrightsmedia.com. Seems to answer some of my questions but this is from the company that is having issues, so I am taking it with a grain of salt.
Internet reviews/reports on the JR Carbine can vary significantly. This is due, in part, to the fact that some reviews predate our improvements while others are more current. The improvements we have made include moving from a fixed extractor to a live one, adding a feed ramp to the magazine well, and adjusting the angle and height of the magazine relative to the bolt. Additionally, we have completely redesigned the bolt, charging handle and buffer system.
We were not happy with the tolerances to which our receivers, bolts, and hammer/trigger/disconnector sets were initially being manufactured. Over time we identified and changed to vendors who can consistently produce these parts to the specifications we require. The end result is a JR Carbine that is much improved over the earlier versions. For those who have purchased earlier versions we have provided no-charge upgrades (i.e. our rapid fire bolt upgrade posted on our website). This has included complete receiver exchanges for the earliest versions.
Following are some of the issues you may have read about and what we have done to resolve them:
General Development - Buffer System
The 9mm JR Carbine was the first model we developed, and we went through about 80 percent of our R&D growing pains with it. We originally used the standard aluminum AR-15 buffer, with a carbine-length spring and a steel spacer in the base of the buffer tube to prevent bolt overtravel. The failure of our initial vendors to supply us with bolts, receivers, etc., manufactured to our design tolerances resulted in increased friction during cycling of the bolt during firing. With the greater frictional losses we were experiencing the standard buffer was sufficient in the 9mm.
When we developed the 40S&W model we noted that the polymer ends of the AR-15 buffers were deforming after a few dozen rounds. In order to counteract the problem we replaced the steel spacer in the buttstock with a rubber bumper to absorb shock and a nylon disc to support the buffer spring and distribute the force of the buffer impact evenly onto the bumper.
By this time, however, we had either changed vendors or gotten existing ones to manufacture to consistently tighter tolerances, resulting in decreased frictional losses during cycling. The net impact of these combined factors was that the standard buffer no longer provided sufficient inertia to slow down the bolt, which was operating at a speed of about 1200-1500 rounds per minute. At that speed the bolt was overspeeding the disconnector, causing 2nd round no-#### occurrences.
We prototyped a solid steel buffer, which really tamed the bolt speed to something manageable, and eventually settled on a buffer weighing in at 7.6 ounces for the 40S&W. We beefed it up a little more for the 45ACP, ending up with a buffer weighing over 8 ounces which works well in the 45ACP and 40S&W, as well as in the lower power 9mm cartridge. (More weight is not possible within the confines of the buffer tube diameter, length, and available travel limits.)
Of course, there is a lower limit to the kind of cartridge that can use this solid buffer. When we develop the .22LR and .22WMR we anticipate reverting to the standard AR-type buffer because those cartridges release so much less energy (22WMR is slightly more than half that of the 9mm, 22LR approximately one quarter).
Light Primer Strikes & Failures to ####
Light primer strikes were caused by a couple of different factors. In our early models the light primer strikes resulted from an internal issue in the original bolt design. In our later models it has been mostly the the result of the hammer following the bolt forward after a preceding round is fired. In these cases either the disconnector/hammer interface wore prematurely and failed to catch the hammer, or the shooter was engaging in extreme rapid fire and outran the bolt - pulling the trigger in a subsequent shot before the bolt was forward and in battery. (Once we discovered premature wear on the trigger group parts, we located a vendor who is able to make consistently high-quality hammers, triggers and disconnectors for us.) In both cases the bolt does not impart enough energy to the firing pin to do anything more than slightly dimple the cartridge primer, if it ever strikes it at all. Between redesigning the bolt and getting trigger group parts that are made of the proper material and correctly dimensioned, the instances of light primer strikes are few and far between. Those that do occur are usually the result of some sort of fouling or extreme rapid fire action - both of which are curable by the shooter by 1) occasional cleaning or 2) not trying to make a semiautomatic direct-blowback gun fire like a fully automatic locking-bolt one.
Failures to Feed/Eject
Our original bolt design employed a solid, fixed extractor that was machined into and integral with the bolt face. It was a novel concept - one no one had ever done before. We designed it for use with American made SAAMI-spec ammunition. Unfortunately, we did not realized how widely the tolerances of pistol ammunition can vary - even among the major ammunition manufacturers. This resulted in some shooters having great shooting experiences because their ammunition was properly dimensioned, while others used poorly dimensioned ammo and had poor shooting experiences. We scrapped the solid extractor design in favor of a live extractor. In the process we made our bolt ambidextrous.
Other feeding problems were resolved by adding a feed ramp to the magazine well, changing the angle of the magazine relative to the bolt, and radiusing the mouth of the chamber and opening up the feed ramp integral to the barrel.
Ejection was improved by changing the angle of the ejector itself and getting both the bolt and ejector plate manufactured to consistently high tolerances.
One issue adversely affecting feeding relates to the magazines we use. Although we have based our initial models on OEM Glock magazines, the quality of those magazines is beyond our control. As most Glock users have experienced, all Glock magazines are not created equal. (To date there have been approximately 8 different generations developed and distributed into the marketplace.) This goes double for aftermarket Glock-compatible magazines. Still, we test fire every JR Carbine before it is shipped and packed. We test each with the magazine it is shipped with, so every magazine we include has also been function tested. We have encountered some variations in the tolerances to which Glock magazines are manufactured. We now include literature pertinent to the particular magazine issues that may arise with each JR Carbine we sell. We have also it on our website.
I am in the process of updating our Safety and Instruction Manual to remove any information that is no longer effective or relevant, and to include new information that we have developed. As soon as it is complete I will update the link to a downloadable PDF copy on our website.
Finally, in addition to failures stemming from extreme rapid fire, we have identified a couple of other malfunction trends that simply stem from shooters' lack of familiarity with this particular firearm. The first involves bent/broken charging handles, the second is feeding and/or operating failures caused by magazine overinsertion.
Many shooters want to install their own favorite M-4 compatible buttstock on their JR Carbine. There is no problem with this as long as they follow the guidance given in our manual. Often they assume that they can swap entire buttstock assemblies and don't bother reading the manual. Unfortunately for them the similarity between M-4 buttstock assemblies and the JR Carbine buttstock assembly is limited to the stock body and,perhaps, the buffer tube. Our buffer system inside the JR Carbine is entirely proprietary. Proper operation of the system relies on certain dimensions being maintained even if the shooter does remember to transfer the internals from the buttstock assembly provided to the new one they are installing. Failure to both transfer the buffer internals to the new buffer tube and maintian proper operational dimensions will result in a bent or broken charging handle after just one shot.
A very large number of us were trained to shoot during military service. Part of that training has usually included the instruction (at least with the M-16/M-4 and M1911/M9) to insert the magazine in the magazine well and slap it home to make sure it is properly seated. Those without formal military training have nevertheless probably seen countless examples of this procedures in movies and on television.
Slapping the bottom of a magazine is no problem when a firearm incorporates internal stops to prevent overinsertion. Unfortunately, the design parameters of the JR Carbine make it very difficult to incorporate an internal magazine stop. Even if one could be designed, it would likely be very expensive and too complicated to operate reliably. (Think Rube Goldberg.) In the JR Carbine the magazine catch is what locks and locates the magazine at the proper height within the magazine well. Slapping it upward into the magazine well - especially with the bolt locked to the rear - can overrun the magazine catch, damage the magazine, and insert the magazine too far into the path of the bolt. While our manual has always included instructions for the proper insertion of the magazine, we will also include a more pronounced warning against magazine slap in the upcoming version.
I hope this answers your questions.
Anyone care to weigh in?
