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AR Lower--from wood!
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  jacattak

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Posted: October 03 2008 at 1:30am | IP Logged Quote jacattak

Agreed, pine is way too soft, black walnut is a good choice, one could also use cherry, tight grained and quite strong. Another choice, although somewhat difficult to work, is purpleheart. VERY strong (a cousin to ebony) and beautifully purple, yes PURPLE, when cleared. Oak and Ash are good woods but thier open grains and large pores would make them a bad choice. Bloodwood would also be good, but I would suggest using the suggested pin sleeves since it is a little prone to splintering at thin points that run with the grain. A good tight grained hard maple would also be a great choice, good workability and great strength.

just my .02

later jacattak

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  orions_hammer

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Posted: October 04 2008 at 7:37pm | IP Logged Quote orions_hammer

Ladies and gentlemen, Farther North Tacticrap is proud to present...


The Pine A.B.O.R.T.I.O.N. is the new choice of the discerning suburban operator for mission-critical tactical plinking operations:


Amazingly, the Pine A.B.O.R.T.I.O.N. actually fires more than once, as shown in this high-round-count remote torture test in our outdoor lab.  Granted, the Pine A.B.O.R.T.I.O.N. receiver cracked and the bolt jammed up after firing the second round in the string, and third total round for the receiver, but this sort of reliability far exceeds that required by the typical mall ninja.

Here's a frame-by-frame analysis of our prototype's first and last actual semi-auto operation:

Gun fires.  Flash hider does its job too well to see anything.


Bolt flies back, extracting empty case.
The whole remote-test jig also visibly jumps back about 1/2".


Empty case flies out of the ejection port at blur velocity.


Empty case visible as a ^^^ blur in bottom of frame.


Bolt blurring as it closes, stripping the next round from the magazine.


Bolt is back in battery, ready for the second shot.

Boy, wood is sure an ill-suited material for an AR receiver!  I trimmed just enough wood to be super happy with the fit of the upper receiver, but my homemade upper mounting pins were a rather tight fit.  Rather than file them down in my drill press (the poor man's lathe) like I should have, I instead tried to gently tap the front pin in with a hammer, which instantly resulted in both front upper mounting ears cracking in half.


Ouch!  dcorb's prediction was absolutely correct!  It's not clear how to fix this, either--you've only got 1/8" of clearance between the pin and the receiver to work with, and this wood just doesn't have the tensile strength to hold the upper down properly.  And this is with a double-width mounting ear compared to milspec, and without the milspec holes for detent pins, etc.  To hold the upper down reliably, I think you'd need a little metal brace of some sort, for example a little sheet-metal piece that wraps around the whole front of the magazine area.

But surprisingly, the rear upper mounting pin went in fine, and amazingly the rear mounting pin alone actually seems to hold the rifle together more or less adequately:


That's when I hit my second major snag.  The (surprisingly long) AR bolt is supposed to travel way back into the shoulder stock during recoil, moving inside a "buffer tube" built into the stock.  I drilled out a 1" buffer hole in the integrated stock above, but my drill bit wandered pretty darn far off-axis, meaning the upper receiver and buffer tube hole weren't in a straight line.

Net result?  The bolt jammed up against the side of the buffer tube about 1" out of battery.  I tried opening up the buffer tube a little with a bigger drill bit, but it's almost impossible to straighten a crooked hole without using a boring bar.  I have a mill and boring head, but I'd need a way bigger mill to fit the entire stock+receiver under the mill to bore the hole out true.

So I decided to use a more ordinary screw-in shoulder stock with integral buffer tube.  Step one was to chop off the integrated stock:


Now that I could fit the smaller receiver under my mini-mill vertically, I used my dial indicator to orient and clamp the reciever on true vertical, and then bored out the buffer tube hole to 1.130":


Now *without* moving the clamping setup or mill, I used the giant 1 3/16" buffer tube tap to tap out the buffer tube hole.  I turned it by hand, but used the mill to keep it lined up.  If the buffer tube hole goes in crooked, your bolt will jam up while entering the buffer tube hole, so I clamped a little 3/8" pointed rod into the mill for alignment--I'd always wondered what that little hole in the back end of a tap was for!  Because I bored and tapped with the same setup, the hole and threads should be (and are!) coaxial.


Buffer tube hole successfully tapped!


However, note how little wood I have left on the top of the receiver--it's less than 1/8", and there isn't room under the charging handle to add much more than that.  When I screwed in the shoulder stock, it felt pretty solid, but while posing for the "operator" pix above, I noticed the top of the stock mount was cracked:


Time for some tactical reinforcing steel!  (Baling wire!)


The stock cracked in a few more places during firing, until eventually the bolt jammed up after test shot 3.  I think the stock mount is under unusually high stress here due to my missing front mounting pin--any tendancy of the upper to pivot upward is stopped only by the stock mount.  I'm not comfortable shooting the rifle by hand with this sort of failure, since the stock's buffer tube is the only thing that stops the bolt under recoil.


So, experiment complete.

Good things about a wood AR receiver:
  • Wood is light.  My stripped receiver + grip weighs 8 oz.
  • Wood is cheap.  I bought some seasoned hickory for a possible version 2, and it's only about $6 for a receiver-sized piece!  (Of course, aluminum forgings are only $22 on sale.)
  • It's literally a weekend project, if you've got a mill.  Wood mills away very quickly.  Even just using pasted-on templates to drill the holes, I didn't have any location problems--FCG, safety, and magazine latch all fit and fired perfectly on the first try.
  • Wood makes excellent practice for machining a real aluminum receiver.  I learned a huge amount about setup, clamping, and precision while doing this project!
  • The magazine well, pistol grip, and hammer and trigger pins all seem to be strong enough to actually use.
Bad things about a wood AR receiver:
  • Some milspec features, like the bolt catch, would be very weak, and are best left out.  A thin slice of endgrain will usually self-destruct during milling.
  • If you let the wood splinter, it looks like crap!
  • The upper mounting pin holes and buffer tube hole are both not strong enough, at least when built in crappy pine.  There isn't enough clearance around either hole to add much more wood, but some combination of better wood and soaked-in epoxy might bring the tensile strength up to a usable level.  Still, I think a metal insert would be needed for long-term reliable operation.
I sure had a blast building and testing out the Pine A.B.O.R.T.I.O.N., I learned a lot both about machining and the AR, and this project provided me with an excuse to get into on the AR platform.  Now I just need to find (or build) some decent milling clamps, and I can started milling rifles and pistols from actual aluminum forgings.  Finally, I'm also getting excited about building some simple blowback rifle and pistol upper receivers, say in 7.62x25 Tokarev caliber!

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  dcorb

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Posted: October 04 2008 at 8:12pm | IP Logged Quote dcorb

The thing that was the most disturbing to me about the test fire was that white stuff on the ground. Are you in the mountains?

I have the urge to put the garden hoses away and dig out my shovels.
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  orions_hammer

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Posted: October 04 2008 at 10:38pm | IP Logged Quote orions_hammer

I'm not in the mountains, dcorb, I'm in Alaska.  We got our first sticking snow in mid-September this year, which is typical.  And I clear my driveway with a truck-mounted plow, not a shovel! 

At least the creek hasn't frozen up yet!
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  weaponeer

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Posted: October 04 2008 at 10:51pm | IP Logged Quote weaponeer

This build is the most creative I have seen in a long time.
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  weaponeer

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Posted: October 04 2008 at 10:54pm | IP Logged Quote weaponeer

Personally I would like to see a lower made out of ABS plastic wrapped in carbon fiber  
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  bikergunnut

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Posted: October 04 2008 at 11:08pm | IP Logged Quote bikergunnut

orions_hammer wrote:
Biker, I'm imagining a rifled wooden 223 barrel--remember the Mythbusters tree cannon?  (video / synopsis)  Wood's low tensile rupture modulus means you'd be limited to *maybe* 1Kpsi, but you could do it!

Wood definitely works fast and easy.  I've literally got like two (long) evenings in this project, and I'm ready (and itching) to drop the parts in it and test fire!

This is the first I found with a quick look, have you thought about a barrel liner? I don't know if it would hold up to .223 but .22lr (maybe mag?) would be doable for sure and there are .22 conversions out there too. As far as a rifled wood barrel, I would be concerned with density variances as well as pressures. Maybe a sheetmetal insert connecting the pin holes would help with strengthining the front pin hole. I have done test runs with allum before, maybe I'll try wood next time, Great build !!!!!!

http://www.brownells.com/aspx/ns/store/productdetail.aspx?p= 25219

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  gundoctor

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Posted: October 05 2008 at 9:12pm | IP Logged Quote gundoctor

very creative.  I love it.  How about laminating something up?  Maybe use a combination of wood, metal, plastic...........finish with wood on the outside?  Is there some type of scrap carbon fiber sheeting that you could laminate with epoxy to make a lower?
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  gundoctor

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Posted: October 05 2008 at 9:13pm | IP Logged Quote gundoctor

 I really like your test firing jig as well.
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  orions_hammer

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Posted: October 06 2008 at 5:57pm | IP Logged Quote orions_hammer

Thanks for the compliments, everybody!  As a kid, Mom would always struggle to find way to compliment my bizarre constructions: "that's very... er... creative!"

Biker's idea of a wooden upper is definitely a good one--and you could stain them in complementary colors too!  It seems like wood trunnions should be strong enough to directly hold the barrel for any lower-powered round, such as in a blowback action.

I had been trying to decide whether to repeat my failed experiment with stronger wood (such as my block of hickory) or just do it right with milspec aluminum, when I started thinking about plastics.  Thick chunks of solid plastic are tough to find, and they're expensive, but 1/2" high-density polyethylene cutting boards are everywhere, and three stacked sheets would be just about the right width for an AR receiver.  You could even pre-mill out the middle sheet with gaps for the upper mounting pockets, magazine well, and fire control group!  Anybody done any milling on polyethylene?  I've had good results cutting and drilling it, and it's pretty strong stuff.

I'd need to join the three sheets together solidly, and I've had screws pull out of polyethylene, and no solvent really works on the stuff, so it'd have to be welding.  I'm going to have to see if I can face-weld two polyethylene sheets using a hot air gun...
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  bikergunnut

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Posted: October 06 2008 at 7:21pm | IP Logged Quote bikergunnut

I really like wood on a gun, an entire wood gun would have been great. If you insist on changing materials.....a guy I knew in high school made an electric guitar out of clear acrylic .
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  Mr.BCH

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Posted: October 06 2008 at 7:43pm | IP Logged Quote Mr.BCH

This was a fascinating project to follow.  Great worksmanship, too!  It starts a few wheels turning in my head.  Very quick, too... unlike some of my own 'projects'  This reminded me of a Clint Eastwood/John Malcovich/Renee Russo movie where JM's character built the 2 shot derringer out of ABS I think... (what was the name?)

I think for a carbon wrapped receiver (great idea for a test), you would need to use aluminum insets for the take down pivots.  While carbon fiber is strong in many aspects, it isn't usually used as pivot points anywhere (Boss, think of those carbon race rims built around forged aluminum hubs).  Still do-able I think.  A friend and I built a complete stand up jet ski hull in the living room of my rental house one winter and used inserts everywhere.  Hmmmm....

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  dcorb

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Posted: October 06 2008 at 8:08pm | IP Logged Quote dcorb

I really like this idea of build with out of the normal materials. I think a laminated receiver using plastic and aluminum sheets would be really cool. I might just have to add this to my list of projects.
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  Branny

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Posted: October 06 2008 at 10:05pm | IP Logged Quote Branny

Need to build something different? Than this is for you, it could be constructed with many different materials. Two years ago I finished one using brass plates and brass solid stock, it function well, I did install all lower parts. Only one problem, it was somewhat heavy so I traded with my friend for riding loan motor, which I still have.

 http://www.metalworking.com/DropBox/AR_15_Scratch_Buil t_Receiver.pdf

 http://news.webshots.com/album/21698116gBOIFFQsWw#foru m



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  EZFEED

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Posted: October 07 2008 at 3:56am | IP Logged Quote EZFEED

This is freaking awesome! Funny but also very cool

And to think I made jokes about Glocks melting on dashboards.....here is the AR that is succeptible to termite damage!

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  hawcer

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Posted: October 07 2008 at 8:34am | IP Logged Quote hawcer

dcorb wrote:
I really like this idea of build with out of the normal materials. I think a laminated receiver using plastic and aluminum sheets would be really cool. I might just have to add this to my list of projects.

I also like that idea and once thought about attempting it.I was going to use alternating thin layers of aluminum and carbon fiber .If I could have gotten my Solidworks program to slice up a model of an AR receiver into layers it would have been a piece of cake  having a template for each layer.All that would have needed to be done after laminating is cleaning up the edges and tapping the buffer tube hole.

Maybe some day.....

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Posted: October 07 2008 at 9:00am | IP Logged Quote dcorb

hawcer wrote:

dcorb wrote:
I really like this idea of build with out of the normal materials. I think a laminated receiver using plastic and aluminum sheets would be really cool. I might just have to add this to my list of projects.


I also like that idea and once thought about attempting it.I was going to use alternating thin layers of aluminum and carbon fiber .If I could have gotten my Solidworks program to slice up a model of an AR receiver into layers it would have been a piece of cake  having a template for each layer.All that would have needed to be done after laminating is cleaning up the edges and tapping the buffer tube hole.


Maybe some day.....



That really sounds cool. I do not have Solidworks or the know how to operate it. But I am starting to get excited about attempting something like this someday.
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Posted: October 10 2008 at 9:52pm | IP Logged Quote dcorb

I have thinking of making a laminated receiver. I checked the prices of carbon fiber. Out of my price range. I would be up to trying one made out of plexiglass and aluminum layers. If someone could do the solid works slice it up thing this would sound like a fun project. It would give me an excuse to dust of the scroll saw. 
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Posted: October 10 2008 at 9:56pm | IP Logged Quote dcorb

maybe a veneer/aluminum receiver. The solid works slice it up thing would make it happen.
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  hawcer

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Posted: October 11 2008 at 12:00am | IP Logged Quote hawcer

Carbon fiber is really expensive.If you go with fabric instead of sheet/plate form ,it is alot cheaper.Also how thick should the slices be?I was thinking 1/32"...the thinner the slice the more slices you have to make a template for.

I suppose you could use a press to laminate all the slices together,a vacuum bagging system may work even better.

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