80% complete lower Dimension's.

[Thompsonbarrels]

Hello and thank for taking time to read this. I am a CNC Machinist with a small business producing TSMG barrels and antique firearm parts. Recently I acquired an 80% complete lower and jig down at Knob Creek, range and MG shoot. They appear to be a Daytona Tactical, definitely DPMS. I have the jig plates and instructions, my question though revolves around the location of the bolt cavity, I have yet to find two prints online that agree with each other. My jig checks at 3.892" from the center line of the rear pivot, an online drawing shows it at 3.840". rather than use the jigs, I would like to CNC Mill the pocket, so dimensions that are accurate are needed. Any information would be greatly appreciated!

 

thank you,

 

Dave

[shepp]

Dave welcome to the forum feel free to post in the intro section!

 

also have you tried to find you answer here 

https://forum.308ar.com/forum/72-80-lowers/

[JJ109]

Seems kind of odd first post is right on 80% lowers 

[sketch]

If the jig is from the manufacture of the lower id use their dimensions. Measure twice cut once....

Or call/ email

hi dave!

 

[Thompsonbarrels]

Hello shepp, JJ109, and sketch. Yes, this is my first post, because this is my first AR and as I said I am a CNC machinist who can his own work, I am looking for dimensions to confirm the jig. I am surprised at the differences I am finding in dimensions I am finding for the AR10 lower.  I do indeed intend to measure twice and cut once, but hard to do that with discrepancies in dimensions, particularly the length between the rear pivot and beginning of the bolt cavity. The jig plate does have some play between the through holes in the plate and the tapped holes in the jig itself.

 

thanks!

 

Dave

[survivalshop]

  I'm a little confused as to what you are calling the Bolt Cavity on a Lower Receiver . Bolt Catch maybe ?

 If you can go to a Dealer or a stocking shop & see if they will let you take some measurements from a striped Lower Receiver or one of our trusted Machinist on this sight , of course .

[JJ109]

Dave, 

Sorry just seemed a little odd. Welcome to the forum. Lot of knowledgeable people here willing to help. 

[JJ109]

Found this on goggle not sure if this will help you. Its in a pdf file. 

AR-Jig-Instructions.pdf

[Toolndie7]

Dave I assume your gonna just run this in the mill correct? Ive got cad files if you tell me what your looking for.  Armalite and dpms have differences.

[Thompsonbarrels]

5 hours ago, Toolndie7 said:

Dave I assume your gonna just run this in the mill correct? Ive got cad files if you tell me what your looking for.  Armalite and dpms have differences.

Hello Toolndie7, I am a CNC machinist toolmaker. I have a DPMS style 80% lower and jog, which I believe came from Daytona Tactical ( I bought them, both the jig and incomplete lower receiver at Knob Creek ). The jig plate has a bit of play, have measured it on the jig, and got dimensions, but they are different by nearly .050" from prints I find online, wanting to make sure I Mill it correctly! If can see your DPMS CAD file, I would greatly appreciate it.

 

thank you!

 

Dave

[Thompsonbarrels]

8 hours ago, survivalshop said:

  I'm a little confused as to what you are calling the Bolt Cavity on a Lower Receiver . Bolt Catch maybe ?

 If you can go to a Dealer or a stocking shop & see if they will let you take some measurements from a striped Lower Receiver or one of our trusted Machinist on this sight , of course .

survivalshop-

                           I am referring to the pocket that must me formed that is .690" wide at the rear, it's location in reference to the rear pivot is what I am concerned about.or put another way, where the two step pocket that must be formed, is located " fore and aft".

 

thank you!

 

Dave

[Thompsonbarrels]

5 hours ago, JJ109 said:

Found this on goggle not sure if this will help you. Its in a pdf file. 

AR-Jig-Instructions.pdf

Thanks JJ109, got those with the jig, please see my other recent posts.

 

Dave

[JJ109]

3 hours ago, Thompsonbarrels said:

survivalshop-

                           I am referring to the pocket that must me formed that is .690" wide at the rear, it's location in reference to the rear pivot is what I am concerned about.or put another way, where the two step pocket that must be formed, is located " fore and aft".

 

thank you!

 

Dave

The pocket you are referring to is the rear take down pocket. Majority of 80% lower receivers  ar 15 rear take down pockets are already done for you. Majority of 80% LR308 or ar10 lower receivers aren't finished. The depth is in the instructions you have. Which is 0.625" from the top of the lower receiver. 

[JJ109]

Dave i can tell you this much. The dimensions arent as critical as you think. I know this for a fact. My buddy recently did his 80% lower on his AR15. We were at the range and removed the rear take down pin. 

It looked like he scooped out the FCG pocket with a spoon. I asked him if he shot it yet. He said he had 50 rounds thru it already.He also went thru the front of the FCG pocket and the mag release spring was exposed to see. I was going to take a pic with my phone just so people can see how bad a lower can be done and still work. He was embarrass and closed the gun up. He has had zero problems with it. 

I still break his balls everytime i see it!

Edited November 10, 2016 by JJ109

[sketch]

^ Pic or bs! Thats how it works!

breaking balls is hard to hit if there marbles! Put them in a sack! 

[JJ109]

Sketch ill try just for you buddy.

He wouldnt let me take a pic last time we were out at range. 

He is a good friend of mine but his lower looks like crap inside.

Dave you being a machinist you way ahead of the curve compared to the average person doing 80% lower. 

[98Z5V]

On ‎11‎/‎9‎/‎2016 at 9:33 AM, Thompsonbarrels said:

survivalshop-

                           I am referring to the pocket that must me formed that is .690" wide at the rear, it's location in reference to the rear pivot is what I am concerned about.or put another way, where the two step pocket that must be formed, is located " fore and aft".

 

thank you!

 

Dave

That particular portion of the Fire Control Group pocket isn't important for a semi-auto AR patterned rifle.  If you were manufacturing a full auto AR, it would be important to hit minimum dimension to accept the Full Auto Sear.  Otherwise, it doesn't matter.