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DOCTORDEMO

Rookie with more questions than answers

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Hello everyone,

I'm not sure which rabbit hole I went through to find this place but I've been looking around a little and decided to join in. I'm a retired millwright/machinist, gun enthusiast,  new to the AR /LR platform. 

I have recently completed a 300 blackout build from one of the 80 percent kit suppliers but what I really wanted was a .308 . When I was shopping around there weren't any in stock anywhere so I settled. Moving forward I have a newly acquired .308 LR upper DPMS (style) from one of the big online stores.  

Here is where the fun and questions begin, instead of another 80% do it yourself lower, I have a piece of 7075 sitting in the mill vise and I want to do the whole shebang myself.

Can anybody tell me if the AR-10 and the DPMS share the 3 degree mag well angle to baseline, or is the LR .308 DPMS  mag well cut like the AR-15 ?

I have a drawing that is for an AR-10 .308 that conforms to ASME Y14. 5M -1994 and looks to be very complete and well detailed, and I know it wont work for the LR .308 DPMS due to the difference at the buffer tube area but I can't find any drawings for the lower I am wanting to build. 

Thanks in advance

Steve

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Thanks Swiftab, now that I think about it a little, after the convoluted introduction what I should have asked was : if anyone with DPMS lowers could verify the angle between the mag well and the top of the lower as 90 degrees or something else.

 

Steve

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Only the Armalite AR-10B pattern has the 3* magwell.  The AR-10A pattern is setup for the 0* and the DPMS LR-308 pattern, for the magwell.

Here's some reference information:

https://www.cncguns.com/projects/ar10lower.html

One of the main differences between the AR-10™ and the AR-15 is that the AR-10™ magazine (mag) well in cut at a 3 degree angle.  This would cause a problem for me since this would add an additional 2 operations in the machining of this lower.  It would be fairly difficult to set the receiver up on a 3 degree angle to machine the top side of the mag well and then flip it over on the same 3 degree angle and machine the bottom of the mag well, while trying to match up the mag well cuts.  Like I've said before most companies use an EDM machine to wire cut the mag well, and I thought I'd do the same with this AR-10™.  We don't have an EDM machine at the shop, so I had to have this cut by a local machine shop.  This was pretty expensive to have done, since the guy had to set the EDM machine up and only cut a few receivers.  But I think it was well worth it, since I didn't have to fool with having to figure out a way of cutting the 3 degree mag well. 

Edited by 98Z5V

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1 hour ago, 98Z5V said:

Only the Armalite AR-10B pattern has the 3* magwell.  The AR-10A pattern is setup for the 0* and the DPMS LR-308 pattern, for the magwell.

Here's some reference information:

https://www.cncguns.com/projects/ar10lower.html

 

 

Well, so far, You are the only source that has anything that says 0 deg. for the DPMS specifically. Thank You. The site that you linked actually has the same drawings that I have, but I couldn't find any DPMS information. 

I didn't want to start hacking and hewing away at a lower and find out hours into the process that it was going to be for "the next" build.

So the lower is going to be slightly easier than the 3 deg. mag well debacle, but still a challenging project with a manual mill and no dro. If all else fails I can buy a lower, but what's the fun in that?

 

Steve     

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5 minutes ago, DOCTORDEMO said:

 but I couldn't find any DPMS information.    

DPMS, on the LR-308 pattern, followed the AR15 pattern for all their stuff, minus the dimensional changes needed for the larger magazine, obviously.  .  The only reason the Armalite AR-10B pattern was 3* is because of the magazines that they had to use to make that gun. 

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On 4/21/2021 at 9:21 PM, 98Z5V said:

DPMS, on the LR-308 pattern, followed the AR15 pattern for all their stuff, minus the dimensional changes needed for the larger magazine, obviously.  .  The only reason the Armalite AR-10B pattern was 3* is because of the magazines that they had to use to make that gun. 

Well, I compared the AR-15 drawings with the AR-10B drawings and did some reverse-dimensioning. Now my reference point is from the take down pin instead of the pivot pin. I also compared the uppers and found that the DPMS 308 and the AR-15 when in battery is nearly identical in the dimension from take down pin to firing pin, so between your comments, the web, and my two uppers I have started making chips.

I know that I could have probably completed the build by now if I would have ordered either a lower or a 80% or a jig but I was looking for a little challenge, although I would have thought drawings for the DPMS would have been as easy to come by as the other platforms out there. I might be a little stubborn also.

Being totally new here, should I continue this thread here, or start a new one as this build moves forward?     

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1 minute ago, DOCTORDEMO said:

Being totally new here, should I continue this thread here, or start a new one as this build moves forward?     

Your call - but you're moving with info, so this isn't a bad thing. 

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