Dear Michael,
Thank you for bringing this to our attention.  From the thread, it does
sound like this individual received one of the first production (50) J R
Carbines.  The components were retained by take down pins, and the Quad
rail was slightly undersized.  The J R Carbine has been upgraded & the
new production models have the upgrades.  Here is information provided
by the folks at Just Right Carbines explaining the changes/upgrades.
All that the guy needs to do from the forum is contact EMF and we will
send a return label for him to have his carbine exchanged for one of the
new ones.  We have been unable to sign on the AR-15 site to respond to
the post or let him know.


..."Probably the first difference one would notice in a side-by-side
comparison of your carbine and the enhanced version is the method by
which the trigger housing and magazine well are attached to the
receiver.  Our initial attachment method consisted of posts machined
into the receiver.  The posts are made to fit into recesses in the
trigger housing and mag well and were secured together with pins running
transversely through the posts, locking them into place.  The pins
themselves were grooved circumferentially in the center and kept from
moving laterally by a ball detent in the bottom center of the receiver
posts.  This arrangement proved a bit more cumbersome - and expensive -
than we wanted.  Also, machining tolerances proved to be difficult to
maintain to ensure correct fit so the fit did not feel loose or too
tight.


The current carbine continues to employ the post/recess attachment
method.  This is inherently a very secure way to mate the three central
parts and stabilize them into a single unified unit.  However, instead
of using pins to attaching the trigger housing and mag well to the
receiver, we now accomplish the task with 10-32 flat head hex machine
screws counterbored flush. In doing so we reduced the overall part count
by three (eliminating the ball detent in each of the receiver's three
posts) and mated the parts in more secure, solid manner.


The second major change involves the ejection port area of the receiver.
While the J R Carbine is designed to be a multi-caliber firearm, we
based our initial development on the 9mm Parabellum cartridge because
the feeding and ejection tolerances are a bit more critical on the
smaller caliber than on the larger ones.  Working out the engineering
for the 9mm made doing the same for the .40 S&W and .45 ACP easier to
accomplish.  We discovered, however, that we needed to increase the
inside height of the ejection port area of the receiver to facilitate
ejection of the larger diameter cartridges/casings and to avoid
occasional stovepiping.  Current production receivers now have that
dimension increased.  We are in the process of retro-machining all of
the earlier model receivers to bring them into the current
specification. 


The third major change involves the replacement of the buffer spring
with one that is shorter in length.  Our first prototypes used AR-15
carbine-length spring.  This provided buffering action as well as
sufficient force to cycle the bolt forward and chamber the next round.
As we smoothed out the carbine's action we were able to reduce the
buffer spring even further to an overall length of 10 inches. 


The fourth change involves the firing pin and firing pin spring.  When
we first began developing the J R Carbine we chose to incorporate as
many existing stock parts into the design.  We did this for two reasons.
First, the stock parts were readily available from numerous sources.
Second, they were parts that were already thoroughly tested and proven
reliable.  With that in mind, two items we incorporated off-the-shelf
were the firing pin and firing pin spring - both originally for the 1911
pistol.  While both worked well, in the course of continued testing we
determined that we needed to modify each in light of the way they were
incorporated into our particular bolt design.


The 1911 firing pin spring is turned to a slightly smaller diameter on
one end, which is intended to grip the upper shank of the firing pin and
keep the two parts mated by friction.  We discovered that our bolt
handle, which is able to touch the firing pin/spring assembly as it
rests in the bolt, occasionally caused the firing pin spring to slide
downward off the shoulder of the upper shank, effectively preloading the
spring and resulting in light primer hits.  We have since reversed the
direction of the firing pin spring, placing the larger end of the spring
onto the firing pin so that it remains loose on the firing pin.  Any
occasional contact the bolt handle might have with the firing pin spring
while firing and cycling the action no longer shifts the spring's
position relative to the firing pin, eliminating any light hits.  We
also changed the shape of the upper end of the firing pin, eliminating a
small but pronounced shoulder that also had the potential to
intermittently interfere with the bolt handle.

You may have noticed that the J R Carbine utilizes the trigger, hammer,
safety selector switch, and overall geometry of the AR-15 trigger group.
Again, this is a proven design and in the public domain with many
producers of the same parts, so it was a natural fit.  Unfortunately, we
experienced some sporadic problems with some of the hammers in our early
production carbines.  The J-springs on many of the hammers supplied by
our initial vendor were out of spec.  This permitted the hammer pin to
creep laterally while firing - to the point that the hammer became
misaligned and the gun would fire a 2-round burst before the hammer
became too misaligned to fire at all.  We have worked with our vendors
to correct that problem." 

 
As you can see, the folks at Just Right Carbine, LLC have made
significant improvements to this carbine. Since the above was provided
to us, they have made a few additional changes which should also correct
any issues with this carbine.

We appreciate your continued support.
Sincerely,

Debbie Sims
Director of Operations
EMF Company, Inc.
(800) 430-1310