I tried this in the "Build It Yourself" forum and did not get a single response so I will ask here......

I am looking for the 80% machining information for a 308 DPMS (LR-308) style lower. A solid model and a dimensional print would be great but an AutoCAD drawing or even PDF would also work. I have found two PDF drawings and they do not agree on the location of the trigger holes relative to the front takedown hole, there is a .020 variation between a Quentin Defense print and a SSI print. I do not plan on using a fixture so I need the numbers.

What are the differences between the two platforms besides the  the buffer tower, 308 has a radius ane the AR10has an angle.

AR-10B uses an angled mag well (3.0 degrees from vertical), because it essentially uses M14 magazines that have a different catch slot location and follower. The spacing of the trigger holes relative to each other will be the same, but their relation to the bolt catch and other things will be different. (They also use different BCGs, barrel extensions, receiver extensions..)

You can search all year for prints on the LR308 pattern but what you will find is a lot of stuff not matching up, because they were reverse engineered from something slightly different, not measured quite the same, not measured from the same datum, referenced to something different, utilizing different features/dimension altogether.

If it is a Quentin Defense 80%, use their print. Really, for the holes I would indicate from the top mating surface of the receiver and the center of the safety selector detent hole. You could also indicate from the pivot hole and verify it with the detent hole when you cut the .375" safety selector hole. The FCG and lug pockets are mostly for clearance, but the hammer travel and clearance could be restricted if it is screwed up a lot. 3.840" from the center of pivot hole to first wall of FCG pocket should be correct (as the SSI print shows.. I have another print from Illirian Engineering that says 3.838", when adding two dimensions anyway, close enough). Indicating from pivot point will conform to most prints, and make you feel warm and fuzzy inside since you used the same feature as a datum for both operations.

The only 80% LR308 I machined was from an H&H Tactical (was not very impressed with quality but I got it fairly cheap) paper weight, they clearly used the SSI computer model to machine their lowers so it wasn't much trouble to use that print and reference it to others as reassurance. Some prints will show .630" depth for lug pocket, others .520"-.525", either should be fine, .525" is probably more correct. .630" is from the AR-15.

Well put and on point...Thanks.

Thanks Dark Drifter for filling me in on the fact that 308 DPMS prints are not only hard to come by, there are several variations.  Your info coupled with the newly tacked entry in this forum, AR10 History, I understand that building a 308/AR10 needs to be carefully researched. I think what I come away with is that the only way to be safe is to buy the upper and lower receivers as well as the BCG from the same manufacturer. It is also good advice you give that to machine an 80% 308, I will start with the selector detent hole that is already in the 80%er and work from there and the top of the receiver. I was hoping that the 80% manufacturer could provide the print but I guess they want to sell a jig and I do not plan on doing it that way.

DPMS lower prints in PDF...

http://www.theflatspot.net/uploads/6/9/0/0/6900641/dpms_308.pdf

That would be the "rifleconnection.com" print, swiped by that website, they even put a white box over the title block etc.

Again, reverse engineered, dimensioned differently.. drawn just last year.