AR 80% lower finishing - Order of operations?

[catoctin]

This take-down pin set screw setup deal seems to be pretty good. The design is using 1/2" long 1/4-28 version of these:
http://www.mcmaster.com/#set-screws/=uwt09x
and a 1/4" long one of these as a locker:
http://www.mcmaster.com/#set-screws/=uwt9ai

It is drilled/threaded from the bottom centered on the take-down pin. The drilling operation goes through the end of the AR handle tab up. I have built four different AR's and with upper assemblies from different vendors. The last one was a bit sloppy and was considering getting oversize pins from Brownells. This would probably help take up the slop.
-Joe

Those lowers from Broken Arms look interesting and I'll be looking for your assessment once it's in your hands. Will you have to modify your clamps/holders for the more angular shape of the lower or are they still within "spec"? Their use of a set screw to take up the slop between the upper and lower is "interesting" to say the least but I'm not sure I am getting my head around just how it functions. Does it just put pressure on the upper's "take-down" tab?

 

[Old Iron]

I didn't drill the wholes just marked with a black sharpie and milled it. I also milled mine to M16 specks. Except drilling the auto sear wholes.

I've built 4 2 in 5.56 and 2 in 7.62X39, The only thing I regret in doing one in a carbine length. That was just plain dumb. I like the 20" heavy A2 military 1 on 8 Oh well live and learn.

Paul

 

[JohnsonFabrication]

+1 on Tactical Machining products, I have been buying things off and on from them for several years now, did a few 80% AR lowers, and i have their generation 2 jig, but frankly, all i did with it was use it to scribe the top of the lower for where it needs machined, then took the jig off so i could see the scribed line.

 

[ScrapMetal]

Update on the lower.

Sorry it took so long, been kind of busy as of late. I did get the insides of the trigger/hammer cavities painted with the Aluma-Hyde but not quite as nicely as I'd hoped. The Aluma-Hyde II is great stuff and I love the finish (it matches the black oxide finish on the outside perfectly). My problem with getting a perfect coat were just "physical" issues with trying to spray paint the inside of a narrow, deep blind hole. The trigger area came out pretty good after the second coat but the take-down pin area was still a little "thin". The stuff sprays on pretty thick and I didn't want to try a third coat for fear of making it too thick in other areas.

FWIW - I think the next time I try using it I'll get the liquid version instead of the aerosol, use the thinning agent to get it to a better consistency, and spray it on using an airbrush.

Here is a finished lower waiting for the upper assembly to show up.



It'll end up being in a carbine configuration, 7.62x39, with Magpul furniture. I've got some fold-down tritium rear and front battle sights from Troy Industries to top it off. I'm also planning on some kind of optics but haven't quite decided on what, maybe Aimpoint...

-Ron

 

[OldMachinist]

I just finished one the other day. Had to drag out my old pantograph engraver to mark it. Haven't used it in the last 20 years so the engravings didn't come out as nice as I'd like. It was a little shallow in places and that didn't show up until I bead blasted it.

 

[ScrapMetal]

I really like the engraving, it gives it character even if it might not be "perfect". I really don't need a pantograph but you've sure got me thinking about making one for my next couple of builds.

Thanks,

-Ron

 

[Old Iron]

You guys should get a Bump Stock and have a little fun. There on sale for 99 bucks they really work great on the 7.62X39 can empty a 30 round mag in about 10 seconds or less. Anyway at least there legal for now. Will work on the 5.56 carbine but the 20" is a little bit to heavy I guess, Haven't worked with it on there very much. Looks like the sale is over there 149.99 now but still cheaper than the slide stock. I don't get any thing off of them I'm just very happy with the one I have. I also build a AR pistol but didn't take any pictures of it.
http://www.bumpfiresystems.com/

Paul

 

[OldMachinist]

I really like the engraving, it gives it character even if it might not be "perfect". I really don't need a pantograph but you've sure got me thinking about making one for my next couple of builds.

Thanks,

-Ron

You could send me the lowers before any fire control machining and I'd do the engraving.

 

[ScrapMetal]

That's a great offer Don. Thanks much! I'll keep that in mind.

-Ron

 

[ScrapMetal]

It occurred to me (I'm a little "slow" ) that I didn't post the completion of the project. Here is the gun/lower in it's final form:


I finished it up with Troy Industries folding battle sights, front and rear (in the lower picture the eyepiece is moved to the side in order to raise the rear sight), an EoTech holographic sight and magnifier, and all Magpul furniture. The Troy battle sight is high enough so that it can be used without removing the EoTech sight though it might not look it from the pictures.



I have three 20-round and three 10-round of AR-Stoner magazines that I got from MidwayUSA. Five of the magazines perform perfectly. The sixth looks like it was from older stock (different follower) and the lip wasn't milled correctly so the rounds won't feed from it. I expect that once I file down the front lip that problem will be gone.

All in all it shoots great and is a really fun gun to shoot. So far I've got about a thousand rounds through it with nary a hiccup. This one's gonna be a keeper.

-Ron