View Full Version : Legality of 80% ABS Lower + 20% PVA/HIPS

06-10-2013, 11:26 AM
Seeing the launch of a company dedicated to all-polymer 80% lowers (http://polymer80.com/) inspired me to think of ways to lower the difficulty required to complete an 80% lower.

If someone were to create an 80% lower, with the 20% filled in with water-soluble PVA or HIPS (this requires an FFF printer with dual extruders), would that be legally considered a firearm?
All the user would have to do is dunk the lower in water, and their 80% lower would turn into a fully-functioning lower.

Here's a maker who uses PLA/HIPS as water-soluble support material: http://www.thingiverse.com/thing:12342

Here's a good FAQ about 80% lowers: http://www.tacticalmachining.com/80-lower-receiver.html

It seems like the legality of existing 80% lowers is due to the fact that converting an 80% lower to a 100% lower requires "specialized skills and tooling"

A lot of questions have been raised about how our 80% AR-15 Lower Receivers can be considered non-firearms. We've received a determination letter from the ATF stating that the ATF does not view this as a firearm because to complete the receiver it requires specialized skills and tooling.

I guess we won't get a definitive answer until someone mails a sample to the BATF, but I'm curious to hear your thoughts.

06-10-2013, 12:22 PM
I think someone brought this up before, but I would say no, as it would be so simple to change they would not allow it. But, we'll never know until someone sends to the BATF.

By the way, is polymer80 using Defcad designs? Just curious.

06-10-2013, 01:07 PM
"This jig makes cutting your new 80%, polymer lower receiver so easy, even the average non enthusiast can do it!"

I saw in the link you posted in channel yesterday (but can not find it now) that they provide a jig and drill bits and that it requires nothing more than a hand drill to complete.
In other words, it's simple for anybody with no special skills and only the cheap jig is a 'special tooling'.
The ATF letter has no relationship to the facts.
But they have a letter that says what it says.

06-10-2013, 07:03 PM
> If you choose to utilize the jig more than once, you take the risk of voiding the warranty.

So if you use this jig, which is only warranted to work once, more than once, they will not honor the warranty for the first time you used it?


06-12-2013, 12:16 PM
After doing a bit more research, It seems the two possible material combinations are PLA/PVA or ABS/HIPS. It looks like PVA doesn't adhere well to ABS.

The (legal) advantage to HIPS is it is not water-soluble. Instead, it requires a chemical called limonene. Fortunately, it's safe, cheap, and easy to buy.

Would this be considered "special skills and tooling" ?

More info can be found here:

06-12-2013, 04:27 PM
I don't think they'd qualify dropping a part in a bucket with a solution in it as special skills or tooling. Also, now that this has been mentioned in a public forum you can be sure they know about these alternative processes and will test for it.

It really isn't too much to ask for someone to use a hotknife to finish their lower. Cheap and easy to use.

Have Blue
06-12-2013, 11:08 PM
Also, limolene will attack the base ABS as well and soften it (just not as quickly as the HIPS). Soluble support would be better done with PLA: http://ifeelbeta.de/index.php/support/support-full-disclosure

Have Blue
06-28-2013, 08:50 AM
Just saw this - looks like another company has come out with an 80% polymer lower:

07-10-2013, 05:35 AM
Any pick up one of those EP Lowers 80% polymer lowers yet? They look to be selling well and the company has a multitude of colors. They have video of one guy finishing his in under an hour with a Dremal and a knife.

I can't order one being in a firearm free country, but I plan on picking up a couple when I get back to the states.