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Building another large frame ar


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I started this dmr last week on the cheap. I went to the gun store and they have a used bargain barrel of parts. I found the ergo stock for $20, the hogue grip for $5 and the odin rail with no barrel nut or other hardware for $25. (Amazing how a few parts can bring on the build. I went to my regular spot to buy the rest of the parts and they gave me the barrel nut and hardware for free. The bill for the rest of the parts: aero upper and bcg, geissle 2 stage, faxon 20" fluted 5r barrel were about $800, and I had an .80 lower and all the spare odds and ends in my junk box. All in less the optic...I'm at less than $900 for a nice rifle.

I ordered a primary arms 3-18x50 .308 acss HUD dmr scope today. I still need to mil the lower and hopefully it will be a nice rifle.  


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I got the PA 3-18×50 and I'm impressed for the price. Obviously I haven't shot with it yet. I have an issue with the .80 lower. I bought at a gun show years ago because it was cheap but the guy didn't know what kind it was and he didn't have a jig...so it ended up in the junk box. None of the jigs I have fit it. Anyone have any info on milling without a jig? All I've found online seems to require a CNC machine and machining knowledge.  I've always used a drill press and have no machining skills or knowledge. 


Edited by MrPaul
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I use the Ray Vin plates with an extra set of shims to shore things up. Mine were milled from plywood on my drill press (milling bit). They required a very small amount of extra milling to work on the larger frame lowers (still works with the AR-15 after the fact). I can't find them off hand, but know I posted pictures around here somewhere...

I can certainly point you in the right direction if you have any questions about the drill press setup; I simply use a compound table and vice bolted on. It is possible with just a vice and press of course. The real fun here is determining where the pocket needs to be cut (accurately). Even more-so in terms of accuracy with the FCG pin holes. 

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Thought a little more about this; and it shouldn't be tough to get that up and running. The measurement I used in setting up the pocket location was the back of bolt catch slot, to front of FCG pocket measurement. You simply need to compare against the lower of someone running the same kind of upper. DPMS style (those with a radius) lowers have about half a dozen different cut variants; but none of that matters if you're using an upper that wasn't initially compatible. What I'm trying to say is; don't try to use whatever blueprints you find on the internet for this... You just need to ask for the relevant lower measurements that work on that upper. 

I've seen a few measurement polls around here that were very effective and producing required information. I had to ask for the same thing to get my jig-free .308 built and functioning; thanks to @98Z5V in that case. 

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Thanks for the input guys. I have a jigs for .308.. I have a hellfire, m1, and another generic one that I picked up at a gun show but none are compatible with this lower. I guess I'll measure the width of the lowers for those jigs an use the one that's closest to this one.  This lower has the wings that hang over next to where the trigger group goes. I think I just need to get the measurement on the space between the bolt release slot and the front of the firing group pocket and to make sure I get the pocket centered from side to side. I also need to figure out how to level the lower on the drill press so I can work on it.

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Here are images of the Ray Vin plates I used to hold lowers for milling (one is original the other is modified for .308). There is a minor modification from the drawing to fit the .308 lower I did; but being made out of wood it's trivial to add cuts for odd lower features. I typically use shims around the trigger area; so if it's fat there you might not even need to worry about milling out extra on these side plates. 

Here is a link to the original PDF file. I had modified that to make the 1:1 paper templates you see partially glued to my plates (it's not quite to scale in the PDF itself). 


That's how I've held lowers level on my drill press.



Edited by Lane
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Here is my scale drawing if that helps anyone; as well as the original plans inline. The scale drawing can be printed on paper 1:1 if printed at 100% size. Most print dialogs will default to fill the page, which you DO NOT want to do in this case. 

The image shows the one modification I made for .308 lowers as the dotted orange line. Simply extend that trough to fit the lower. 


DrawingsScale.pdf drawings.pdf

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You can certainly make this work. As I mentioned before; I use some 1/8" shims to shore up the trigger area when using these side plates. You noted; it's fast an easy to match up to the lower and see where else you need to cut for something a little different.

Take your time and enjoy that vacation; I just wanted to post this stuff while I was thinking about it. Some of it I hadn't shared before... This actually inspired me to clean off my drill press and get a few final cuts done on one of my builds.

I went back and read through your build parts; looks like you have an Aero Precision upper; you should have no problem getting that measurement from a few lowers around here. I personally will be interested to see how it matches up with the variety of DPMS style FCG cuts that are published.

Measurement poll: Aero Precision .308 lower; back of bolt catch slot, to front of FCG pocket. Might as well measure pocket depth if you have calipers out. Couldn't tell what to expect for that measurement looking at the product photos on the Aero website...

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