If I purchase and complete an 80% lower, how can it be finish coated and how durable are these coatings compared to an anodized receiver?  Also is there an inexpensive way to get them anodized?

Does anyone have any good links about anodizing?

What about powder coating?

Just thinkin out loud.Dchann

Here's some helpful sites.

www.molyresin.com/
www.concealcarry.org/ar15/bs-home.htm

A decent anodized coating is around 100X more durable than any kind of paint in existence, not to mention much better looking (it will match your upper).

A local anodizing shop is the way to go if you're only doing one lower. Since your completed lower is legally now a firearm under federal law there are some considerations. In most states, if you are on the premesis while your "firearm" is being anodized and dyed, the work is "being done under your supervision" and is legal, even though neither you nor the anodizer are FFL licensees. Technically, if you aren't there the anodizer should hold an FFL for this to be legal.

The otherwise excellent Builder's Squad document has been around for years; however the anodizing method they describe is almost certain to fail miserably, notice that they did. Their conclusion that aluminum casting alloys can't be anodized and dyed sucessfully is nonsense. It is in fact only slightly more involved than forged or barstock alloys, provided that you are anodizing correctly. We at Roderous www.homegunsmith.com anodize and dye cast AR lowers all the time; and they turn out great, but we know what we are doing. Another good source for the correct anodizing procedure is the anodizing forum on www.caswellplating.com you can also get the correct anodizing dyes here, RIT dye is for cloth. Its not that hard to do it right.

I just had some recievers anodized for the min $100 charge at a local place straight out of the yellow pages.  I told them they were rifle recievers and they didn't seem to care or ask any questions.  If you go this route, be prepared for them to ask you for a print, or at least some dimensions and possibly estimated surface area.  

The finish I got was the real deal MIL-A-8625 and they look great.

Thanks,

I'll do some reading now . . .   Dchann

A fully machined AR15 lower calculates (AutoCAD) to 0.5798 square feet in surface area, tell the anodizer 0.58 square feet.

CounterStrike,
Mil-A-8625F covers Type I, Type II, and Type III (hardcoat) anodizing. Which did you get? Type I is too thin to be dyed so its out. Type III is difficult to get a dark black with conventional dyeing. Its probably Type IIB, which is typically 0.7 mils thick and dyes very well. You may have gotten "Type II 1/2", which is Type II grown to Type III thickness (2-3 mils) which is what I use on my own ARs. It looks like Type III, except that the dyeing looks too good.

In spite of commercial claims to the contrary; 99+% of all commercial ARs are Type IIB. Only real US military spec M-16 variants, sold to the govt. under contract by FN and/or Colt are actually Type III, and both vendors have to prove it. It takes a testing lab to tell the difference between Type II and Type III, mere mortals like us would never know the difference.

Well I only know what I was told over the phone before I dropped them off.  According to their tech my quote was for MIL-A-8625 Type III Class II.  We talked abit about the different types and classes and this is what I was told.  What I actually got may not be Type III but I'll never know.  I didn't come across as 'having' to have it so who knows.  My holes did shrink about .001"  

It did dye very well, matching my Armalite upper almost perfectly.  I couldn't be more pleased.  They didn't do a perfect job, there are a few tiny spots that didn't take, not racking marks but just anomolies.  Over all I am very pleased, and glad I gave up on doing it myself.  The $100 spread among six recievers was worth it.  

FWIW if I were doing an 80% AR15 like the guys here I would definately call around for the hell of it and see if you can find a plater to anodize.  The feel of the aluminum from the un-anodized to the anodized made it all worth while.  I don't know how to put it into words, but you can feel the different hardness just by picking it up.  Plus no more rub marks on the mags or other 'gummy' problems.

If you were able to measure a 0.001" decrease in hole diameter it wasn't Type III. A 0.001" reduction would indicate a 0.5 mil (0.0005") anodize thickness, too thin for Type III.  But then again, small holes rarely anodize to the full thickness of large areas. In any event, you did very well at $100 for six lowers.

The apparent hardness you feel is because anodize is a ceramic, alumina (aluminum oxide). Being a ceramic it is brittle and extremely hard, about as hard as silicon carbide. This is the main reason why it is so superior to paint on an aluminum firearm. If you tap on it with a with a small piece of mild steel you will hear the anodic coating  ring like hardened tool steel.

Fibergeek,
If you do a Type III Anodizing, do you need to drill your holes bigger and remove more metal from other close fitting parts before you anodize?  If you do, then by how much?  Otherwise, how would you get the pins to go in and the parts to fit together?

The thickness of the anodized coating is accounted for in the blueprints for both the lower and the parts themselves. If you follow the ordnance prints for hole sizes, and properly drill and ream them, and the anodizer follows the spec for the coating, then the thickness of the coating is already taken into account.

Even if the anodizer exceeds the spec for coating thickness (which is seldomly the case as thickness takes time to grow, which equals $$$) it isn't an issue. Worst case, where the layer is too thick, lube the part well, and using fine sandpaper, lightly sand the interior of the hole. You're talking dimensions on the order of 0.001" or less, so sand very gently. It will remove a little anodization and allow the part to fit.

If you go the professional route, I doubt you'll run into this. Although Mil-spec calls for a minimum of 2mil thickness (0.002" or 50.8microns), part of the definition of Type-III is that it be thicker than 25.4 microns (anything greater than 1mil). Every commercial (i.e. non-military) AR upper/lower I've run into and measured (colt, bushy, rra) have all met this definition of being slightly more than 1mil thick, but none have even come close to being 2mil thick.  You shouldn't have a problem with dimensions, but if you do, its easy to resolve.