Charlie Muggins wrote:3D printing is a very interesting emerging technology but has very restrictive limits with regards to cost, accuracy, durability and accessibility. Interesting things will happen in time with them, and I'm looking at building one, but they are not like your £40 Epson inkjet you can get from Argos. The process for making an AR15 lower is not simply "buy, plug in, print, assemble, shoot". The main practical advantage they offer is that they require less skill to produce a design. That has lead to a lot of their popularity in the "maker" community IMO -- people who haven't learned hands-on skills and can't be bothered to learn them. I see it in electronics side of the "maker" community too; people buying Arduino boards for a task that would be better served with a cheaper, more reliable and physically smaller discrete circuit.
As I recall, don't 3D-printed AR15 lowers have a very limited longevity? Something in the region of 200 rounds. Not exactly earth-shattering when you look at some of the "0% lower" productions from the hobby gunsmiths.
As I'm sure we're all aware a basic SMG is available to anyone with basic metalworking skills, plumbing parts, the tools found in the average garden shed and a spare weekend. Crude .22RF pistols used to be made by crooks from telescoping radio antennae jubilee clipped onto a piece of wood. Mao Mao rebels built slam-fire shotguns from plumbing pipe. All of these are "ghost guns". They are less visible than the featured AR15 due to not having to buy the parts from Brownells, and arguably have a similar longevity.
It just so happens I have a 3d printer, the commercial kind are uber expensive - but mine was 500 quid -
http://www.bq.com/gb/prusa - whilst it's a fairly well designed "kit" and it produces some pretty decent parts on it's highest resolution - there are actually a lot of issues that prevent you making a usuable AR15 lower.
The biggest is to do with the thermal properties of the plastic and the rates of contraction as it cools (glass barrier etc) - you end up with something that looks like an AR15 lower but is out by many tens of thousandths of an inch in just about every direction - so triggers and hammers don't line up, the magwell is as rough as a badgers arse and so on.
Now of course they can be printed - but there'll be a degree of fettling to get something that works...ish, and the life time of it will be limited AND the big one for me - if that lower lets go and the bolt comes whizzing back right into my eye socket (so in the UK we're talking 22 uppers on printed lowers, as the CF uppers are all straight pull S1).
With a commercial printer say using lazer and resin - they it'll be a lot smoother and I'd expect dimensionally more accurate - but, if you can drop 20 grand on a commercial printer, drop it on a CNC mill instead (2nd hand perhaps to get under that budget).
I use my 3d printer for what I think they're really intended - rapid prototyping of a product before you send it of to be injection moulded properly (as per the M&P 15/22 with a polymer lower)
That said - I have thought about 3d printing a cutaway model of an M16A2 showing the workings of the 3 round burst with it's cam etc. A Cutaway in 3d printed lower couldn't actually get me in trouble with the feds in this country could it </sarcasm>