Annika, a reader of TFB, emailed me an idea for an AR-15 upper receiver and asked me if I could post it on the blog to see what y’all thought of it …

I’ve got a pretty straightforward idea that I’m hoping for some feedback
on. If you felt like making a post on this idea in order to get broader
feedback that would be cool, otherwise I’d just appreciate your own take
on it. If it seems like interest in the product would be high then this
could also serve as a petition to the industry in general to create such a
product.

I want to suggest the creation of an inexpensive pistol-caliber AR upper
receiver with a right-side magazine well for accepting Glock mags (for
example). The ejector port could be positioned so as to eject spent cases
down through the lower receiver’s magazine well, and a simple
reciprocating charging handle could be positioned on the left side of the
receiver for manipulation using the supporting hand while maintaining a
standard grip, holding the firearm on target. Otherwise the arrangement
could be flipped so as to somewhat replicate the layout of the Sten.

This arrangement would have the obvious advantage of removing the lower
receiver from consideration when switching between different caliber upper
receivers. No dedicated lower receivers or annoying mag well blocks would
be required. This would also be a largely ambidextrous set-up, with
neutral downward ejection.

I imagine this would be targeted specifically towards shooter with a Slide
Fire Solutions SSAR-15 or other pump-fire stock wanting to shoot pistol
caliber ammunition but not wanting to have to deal with some of the
complication or expense you can currently expect with other compatible
pistol caliber carbines. This would be an entirely self-contained and
simple conversion unit.

In keeping with the overall intent to produce an inexpensive product I
imagine this receiver being constructed of glass reinforced Nylon (like
KelTec’s Zytel) or possibly with stamped sheet metal. If the LMT patent
could somehow be worked around it would be ideal for the handguard to
simply be an extension of the receiver, instead of a separate piece. I
imagine the receiver being manufactured with one top rail for optics and
no included iron-sights. Potentially the receiver could feature a
heavy-profile barrel of, say, 10″ with either the last 6″ milled out for
lighter weight or with a 6″ FH or shroud/extension permanently attached,
discouraging warping from heat generated by high-volume fire while
maintaining a low enough weight for maneuverability and effective use of a
bump-fire stock.

I have no interest in copyrighting, patenting or otherwise legally
claiming permanent ownership of this idea, since my primary interest would
be to see the product go into production in a timely fashion.

Included is a very rough sketch of how I imagine the final product could
look.