Originally Posted by Masked
Do you know anything about steels? Aluminum? Why 4041 is used on most actions? Barrels? Anything?
As a matter of fact, yes Sir, I do. 4041 aluminum is not used in any firearm actions that I'm aware of. Bolts, barrels, and actions for virtually all centerfire-chambered firearms will be steel of varying flavors. Carpenter makes the go-to steels for American-made semi-auto rifles. 4340/4350, 8620, and 4140 are steels of choice for bolt action rifle actions. There is no polymer in existence that can match the material properties of the aforementioned steels that can be 3D printed; all
of them require treating, hardening, and stress relieving. To say that one can be used to create an action for a .408 Cheyenne, itself a 63k PSI round, is a bold-faced lie. It is not possible.
Let me repeat that so that I'm perfectly clear. It is not possible.
This is not an opinion, but material properties (aka, physics). A .408 Cheyenne will explode spectacularly and dangerously if you attempt to use a polymer action for one.
For pistol frames? Maybe. That $1500 printer won't be printing pistol frames safe for use with centerfire handgun rounds though. It can't use the resins strong enough to match what Glock, FN, H&K, et al use in their pistols. That's likely to change in the future; pistol frames are a lot more within the realm of capability of affordable resins. That's not to say it will be easy though, as Glock learned with their third gen .40 S&W compact and full-sized pistols.
Where these printers will be awesome with what can be done now
is in polymer magazines. Again, won't be the same stuff Magpul uses so it won't have the durability, but reliability is a matter of design and geometry. Metal of like wall thickness will still be stronger, but if you could knock out 50 magazines for $500 or less, that puts you in GI magazine prices that you can make at home. That's cool stuff.
It's just not worth saying anything else because you clearly don't comprehend why a BCG/Buffer spring would cause more stress then a forward motion...
You mean how the BCG goes back into the receiver extension, contacts the buffer, compresses the action spring, and ultimately bottoms out against the rear of the receiver extension?
I don't know who you learned what you know about ARs from, but I suspect it's not from the likes of Trey at KAC, Bill Alexander, Mike Pannone, Pat Rogers, Larry Vickers, Kino Davis of Vltor, or Paul Buffoni of Bravo Company. Trey's family helped design the system. Bill Alexander, Kino Davis, and Paul Buffoni helped refine the system in these post-2004-sunset years. Pannone, Rogers, and Vickers wrote the book (one of them literally) on how to use and maintain an AR15. Yes, Sir, I have some knowledge of the platform.
The rear of a to-spec lower receiver where it curves up to the threads for the receiver extension does not flex or compress. Since it does not flex or compress, no stress is put on the takedown pin hole. This is a result of the material properties
of 7075 aluminum. I have never seen or heard of a 7075 aluminum receiver cracking by the takedown pin. I know companies like Olympic Arms, Vulcan Arms, Plum Crazy, and other bottom-feeder AR makers have experienced lower receiver breaks on their non-7075 lower receivers. The crack in your picture is a result of the lower receiver compressing when the BCG, buffer, and action spring bottom out in the receiver extension. Solution? Choose a material that resists compression. Polymers can do it, and will eventually be able to, but the lower receiver is still the lowest-stress critical part of an AR15. It's the only function-related component you can
really replace with polymer.
Those anti-rotation pins are actually interesting and relevant; they're typically solutions to out-of-spec receiver holes. You may want to mull that over for a minute.
AS for an AR10 receiver... different animal altogether. Due to the dimensions they are a bit more stressed than AR15 receivers so it'll be quite a while before polymer can
replace metal in an AR10 lower.
Originally Posted by Masked
I never said a 4473 ever left the FFL.
I have friends that work @ The DESP, ATF and NICS -- This is coming from THEM.
That's nice. When you fill out that 4473, it sits in a specified binder that FFL keeps and never leaves it (excepting investigation or license revocation). Yes, the information can definitely be used to create a registry. No, there is no registry at the moment unless specific to certain few states. When you fill out your 5320 form(s), you are registering a firearm as an NFA firearm and/or notifying the ATF of the transfer of an NFA firearm. (For the sake of other readers, the NFA functions more or less like Shall Issue carry licenses; fill out the forms, pay the fees, a background check is conducted, ye wait, and ye shall receive if nothing in the background check would indicate you cannot legally take possession of the mentioned firearm.)
a registry for NFA firearms. There is not
a registry for non-NFA firearms unless specific to one of a couple States. Manufacturers must by law log every firearm produced, but once they deliver that firearm its existence is documented solely by the transfer papers at FFLs and resellers. A central registry does not exist for the firearms, their points of transit, consumer sale, etc.
I say all of this because the ability to fabricate unregistered firearms are not really a big deal. If you file off serial numbers and identifiers, you make the firearm just as impossible to trace as if you'd fabricated the gun yourself. The criminal application simply isn't there. It is definitely viable for people living in ban states to make their own lower to shoot their otherwise-ban-category firearms, but as we've seen the printed materials still aren't quite there yet. I'd have to check, but I think the jigs and tools to complete an 80% lower are about the same price as a 3D printer, only you'd have a true 7075 lower that will last as long as any other made to correct specs. Tradeoff between ease of making (3D printed is easier and quicker) and durability (resin won't hold a candle to 7075 now or for probably many years).