Billet AR180B Lower, Project Defiant (range report post #92)

HeadDamage said:
If you have gone this far when do you make your own upper?
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You may recall a few months back my building of a new piston system.

Now I've made a new lower receiver.

The idea as that's I am building and proving designs using existing platforms. The idea is that sometime in the future I will build a firearm that is an entirely new design. Not completely new in concept, but not an existing firearm.
 
https://www.dlaskarms.com//popup_image.php?pID=82&osCsid=a00b53821ea4a0234dfb2a6fbc61614fCould you have saved yourself some time by starting with an AR15 raw forging? I see Dlask sells them for $40.00. It has the magwell and recoil tube hole already there. It's not an AR15 receiver until it's finished as such, so could it be finished into an AR180B?

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Grizzlypeg said:
Could you have saved yourself some time by starting with an AR15 raw forging? I see Dlask sells them for $40.00. It has the magwell and recoil tube hole already there. It's not an AR15 receiver until it's finished as such, so could it be finished into an AR180B?
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Nope, wouldn't work at all. Too short and lots of other features don't line up.

The biggest differences are the distance from the barrel center line to the front pivot hole. The AR180B sits a lot lower. This means all the trigger components have to sit lower, as well as the magazine. Then the distance from the mag well to the fire control group is also further back as the AR180B bolt is longer.
 
Well I finally got it out to shoot. Had to do some minor adjustments to the FCG pocket to allow the bolt to go forward enough. As I left out the bolt hold open, the hammer was hitting the material at the front of the FCG pocket before it hit the firing pin.

The good news, the gun will discharge ammunition. The bad news, it won't feed from a magazine. Something is off with my measurements and the magazine sits too low in the receiver. The rounds are being stripped but pushed into the bottom of the upper before they can get to the feed ramps. As well, the upper just isn't sitting right on the lower. It's good at the back, but there is a decent gap up at the front. It's as if my front pivot hole is too high in relation to the top plane of the receiver.

This is a side affect of not having accurate measurements of the upper. I really should have put the upper in the mill and probed it. I'm going of a set of AR18 drawings, so I'm guessing Armalite may have changed something.This is a simple fix, just need to make a custom mag catch the lifts the magazine up a bit.
 
werent ar-18 magazine slightly different than STANAG mags, i remember reading that somewhere but they could be modified to fit ar-15's. maybe the ar18 lower has the mag catch in a slightly different spot?
 
That's not the issue, but yes, AR18 mags had a different style catch. It was a pin, instead of the block type on the AR15. As well, it locked on the other side of the magazine, being a simple spring loaded catch on a pivot. You'll sometimes find AR15 mags with the square notch on one side and a hole on the other. These were built or modified to work in the AR18.
 
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