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Posted: 10/20/2025 8:45:56 PM EDT
[Last Edit: machinehead][Edited]
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hello, im a machinist of 25 years and just finally getting around to doing an 80% i thought we had a forum on here about it. I've read the 80% sticky up top. Are there any other good forums around for 80% ar builds? I have 3 tactical machining lowers and I'm not crazy about them yet. The space between the pivot pin is .506 and takedown is .509 both over the max of the TDP print. It also does not have the little rebate/jog in the back of the takedown pin pocket. so far af=bout 25% of my colt uppers have problems closing on it, i think there is some interference back there. They have yet to respond to my inquiry. Id like an 80% with tighter tolerance in that area and without fire, safe marks and without the tension screw hole. Not bad for $37 each but i really hate starting with out of spec parts. The upper is super wobbly when just on the pivot pin. eta i know you used to be able to get replica engraving done too, IE colt, armalite, FN... who is still able to do it on a virgin 80% https://tacticalmachining.com/ar15/ar15-lower-receivers.html |
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Have you read this thread? A lot of good info in here. AR-15/80-Milling-Info |
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Originally Posted By machinehead: hello, im a machinist of 25 years and just finally getting around to doing an 80% i thought we had a forum on here about it. I've read the 80% sticky up top. Are there any other good forums around for 80% ar builds? I have 3 tactical machining lowers and I'm not crazy about them yet. The space between the pivot pin is .506 and takedown is .509 both over the max of the TDP print. It also does not have the little rebate/jog in the back of the takedown pin pocket. so far af=bout 25% of my colt uppers have problems closing on it, i think there is some interference back there. They have yet to respond to my inquiry. Id like an 80% with tighter tolerance in that area and without fire, safe marks and without the tension screw hole. Not bad for $37 each but i really hate starting with out of spec parts. The upper is super wobbly when just on the pivot pin. eta i know you used to be able to get replica engraving done too, IE colt, armalite, FN... who is still able to do it on a virgin 80% https://tacticalmachining.com/ar15/ar15-lower-receivers.html Sell the ones you have if you don't like them. You don't mention if this was a billet or a forged lower. Billet machines easier then forged. Buy new ones that you believe may be better, and doesn't have the markings. Raw/un-coated lowers will be easier to machine than pre-anodized lowers. After machining and de-burring the lower......assemble it and do a complete function check to verify all components are operating correctly. After it passes the function check, completely strip it down....remove every component, spring, roll pin, etc. If it gets anodized....any small spring or roll pin or hardware will arc flash the aluminum lower. Look for a laser engraver business around where you live. it's easier for the operator to draw or transfer files/pics using software. Some guys that do trophy engraving may also do lowers for people. I've done this a few times for more basic markings. Also look for a place near you to do the anodizing or cerakoting after it's engraved. Most anodizers will do a batch price (like $100 for 3 lowers) vs doing just one, so you should have all your lowers ready to go. Type 3 anodizing is the best, and only comes in black. Have them bead blast the lower prior to anodize for a more uniform and flat finish. If they offer vibratory media tumbling as a de-burring process....do it. It will smooth the edges nicely. . |
Occid Vel Occisus Est !!
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I've got a few of those 80s around here somewhere. Give me a minute to enjoy a Guinness or three and I'll see if I can remember to check one on an upper. |
Disclaimer - OP is bad at knowing things, and might catch on fire.
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
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ok.... two things.... You talk about the space between the pivot pin and..... what? Same question for the rear pin. I went ahead and tried a test fit anyway. Maybe I'll stumble on what you were talking about. EDIT - you're talking about the width of the pocket? Mine show as .50, but that's because I don't have any calipers with three decimal places. AND I just spot checked with a TM 80 and three uppers. New 1/4" milling bits went into the lower holes perfectly. They would not go through the matching holes in a BCM upper at all, kinda made it through a Colt upper while on the lower, and could be convinced to mount a JAKL upper to the lower. I'm suspecting the actual takedown pins are a hair under 0.25". ALSO, it turns out that brand new milling bits are sharp. Not just stupidly sharp, but so stupidly sharp that you aren't quite sure if you're cut or not till blood comes out. Just an FYI for anyone (else) 'creative' enough to think of using milling bits as alignment pins when the real parts are not easily available. |
Disclaimer - OP is bad at knowing things, and might catch on fire.
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
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Originally Posted By Amish_Bill: I just spot checked with a TM 80 and three uppers. New 1/4" milling bits went into the lower holes perfectly. They would not go through the matching holes in a BCM upper at all, kinda made it through a Colt upper while on the lower, and could be convinced to mount a JAKL upper to the lower. I'm suspecting the actual takedown pins are a hair under 0.25". The call out for a raw lower is .251 Now....add type 3 anodizing and that hole becomes .2485 - .249 Take down pins are .247 - .2475 A true .250 cutter will pass through the take down holes on a raw lower, but won't pass through an anodized lower. . |
Occid Vel Occisus Est !!
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Its been lore for some time that companies sell their out of spec as 80s because people put them away and never cut them.. Ive had good luck with cerro forged milspec lowers .. but then you have to engrave and paint.. if you get anodized you can easily laser engrave with a cheap diode laser. |
| Most consistent forged 80% I bought were the Matrix Arms ones. An old thread revival but it seems the 80% AR lower craze is becoming a thing of the past. Just saying there has never been a good supply of old A1 forged 80% lowers and I guess there never will be now. What happened to the early A1 forge dies from companies like SENDRA, Olympic Arms, PWA, and Eagle Arms? Worn out and in the recycle bin of time I guess. |
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Originally Posted By backbencher: @HenryKnoxFineBooks Tactical Machining lowers have been problematic in my Ghost Gunner 3 because I frequently had to enlarge the takedown pocket to get Colt and FM mil uppers to fit. I can't say that any of the 80%s I have done were great on spec except when NoDak sold them. Easiest one for me to do are from Right to Bear. Attached File Attached File Attached File Attached File Attached File |
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Believe it or not, Anderson 80% lowers were mostly what I’ve used with no issues. I purchased their anodized lowers. |
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Originally Posted By IdahoPCCinc: The call out for a raw lower is .251 Now....add type 3 anodizing and that hole becomes .2485 - .249 Take down pins are .247 - .2475 A true .250 cutter will pass through the take down holes on a raw lower, but won't pass through an anodized lower. . The specified anodizing thickness is .0010". Anodizing penetrates the substrate by half the coating thickness, so it only adds .0005" on top. A .2510" hole will end up exactly .2500" |
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Originally Posted By j3_: By new post doesn't look like much is going on with 80% nowadays. Nah.. just most of the questions have been answered. But pls feel free to ask away. Attached File Attached File Attached File |
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