Lane

Yes sir, still waiting to lay hands on it, but at least it shipped today. With any luck I will have it Saturday... I will keep collecting information in the mean time. I have a number of hand drawn measurement documents that I will sort through and post anything that is unique. I will measure the threads for the barrel nut and report back when it arrives (and take pictures for that matter). Hopefully it is either 16 or 18 TPI and not something totally off the wall. I'm pretty clear on the AR-10A / AR-10B differences, it was jtallen1983 that mentioned trying his 10B upper on something else so I simply wanted to verify that for myself. The other mention was in regards to the blueprint I had posted with the 81 date. Clearly not related to this project, but posted in case anyone else finds it useful. Ceratac does indeed specify the PMag specifically, but that already seemed like a given with it being called an SR-762 style lower. I can't imagine anyone going back to the Armalite AR-10B style magazines in a new product. I think my plan at this point is to quiz 5d tactical on the difference with the Ceratac lower first. Some other vendors noted getting their lowers checked for width since that jig isn't supposed to touch the sides of the lower receiver at all. I think the most important question I hope they can answer is if that width was the difference, or if the FCG was in a non-standard location. That way; if I still don't have all the answers I can still contact Ceratac without wearing out their good will before I even get started.

That is the one; and they already took my money so I'm committed. I didn't buy their jig conversion kit because I don't have a 5d tactical jig. The cost of both of those would simply make this way too expensive to justify. That's why I'm doing my best to get a handle on all the different variations. I suspect it really isn't totally proprietary, but that they simply don't want to give away their secret. On the other hand; I don't know how 5d tactical has a jig that covers all other 308s except this one. I guess that I why I had been spitballing earlier that they might have copied something they don't have permission for and it actually does match something else out there.

So I think I gather; none of these prints can help me directly since nobody know what they are. What I can do is measure the lower I receive in the Ceratac kit and post yet another blueprint then if there any differences in the location of the selector detent which sets the FCG location. Otherwise it will then be verified which one of the many layouts this particular kit matches. There is an 80% lower with the Ceratac kit, though some of those blueprints would indeed be sufficient to mill from a solid block.

Thanks. I tried to go back and edit that last post but it didn't work. I realized I had indeed made a few errors as I was piecing together from something I started writing last night. That 1981 print does appear to be the real AR-10B? The other ones in the first post all seem to match some new style AR-10A cut, but beyond that I don't know what they are specifically. My burning question there is if they match the SR-762 / Matrix Aerospace old version, etc. Those two PDFs (AR_10-1 & AR_10-2) match the other image shown and have a date of 2004 if that helps narrow anything down. Looks like my Ceratac 308 kit won't be here this week since it still hasn't shipped yet. I think I'm going to try to use one of the prints to make some plates to help hold the lower in the vise while I'm waiting. Here a shot of the set I use for AR-15s. I'll just modify the template I have to match since it doesn't seem like anyone else has published one yet. Simple, easy to make, and soft enough to give a little if things go horribly awry during the milling process while not marring the lower. It's just plywood with a paper template glued on, then ripped with an end mill to depth.

Here are some of the various 308 drawings I've found 308Lower.pdf

I do believe they "think" they have me bent over a barrel on that jig system. Unfortunately for them I know how to use a ruler and will be happy to share my findings. I watched an Armalite YouTube video today comparing the AR-10A and AR-10B and they stated that the uppers are not compatible between the two. I also had no idea that the AR-10A version didn't come out until 2012 which leads me to some further confusion. One of these sets of blueprints is dated 2004, and another 1981. Does that mean that both are absolutely for the AR-10B style or was someone else making 308 clones that became compatible with the new AR-10A after the fact? I would be curious to know how these prints compare to any of the listed SR-762 compatible units. I will again post below this with some unrelated prints which show comparisons between other variations. AR_10-1.pdf AR_10-2.pdf

That's what I said. I already did HIT IT. So I guess I was wrong about the year, 2015 shows the old style so far as I can tell. Still a lot of reading to do. You are all over this poop though, and I'm glad you care. Do you actually want me to post those files I have? I haven't actually read all the rules here yet. I'm more interested in the content; but so many threads... I'm not sure I will live long enough to read them all...

That all sounds good. I ordered this because, like sluggo1987; I want a very personal hunting gun. Season doesn't open for well over a month so the Fall Shoot might not be too far away. I wanted a 308 because I love the AR-15 platform, and just need some bigger bullets; AK-47s aren't quite enough either. I also just love to build, and can't seem to stop anymore. From what I can tell; without having the kit in hand yet, it is a true SR-762 80% lower in cut. The AR-15 kits from Ceratac are also Cerro Forge 80% lowers, and pristine quality I might add. I simply don't know enough about the 308 uppers to know what else might be going on here. For all I know they actually made their own upper, and aren't lying about the fit and function of other brands. At the moment I simply don't know what to ask them specifically; since they didn't want to release their measurements or specs for the FCG layout the first time I inquired. They do say, "just ask" about compatibility, so I am trying to get a handle on all those measurements beforehand. I'd rather not be have to ask 20 questions and seem like a prick to them. So far they have been very cordial with me. I will try to find the Matrix section you are referring to. I have been reading as much as possible here, and around the web. I really loved reading that chicken contest thread the other day. I got about half way through and though it might still be up in the air; but then you had a very worthy contender show up at the table. This place is awesome, and very specific to these builds; I hope I can hold my own one day. You are welcome to poke fun at my cheapskate mentality buying this Ceratac kit. Wait until you see my milling equipment... The finished product on the other hand. I guess you'll have to wait and see if I have the skills. I had already figured out that the new Matrix stuff isn't the same. I didn't find many pictures of the old ones around; but one really good set was enough to compare visually. jtallen83 mentioned early Matrix; so I was watching out. Anyone have a clue when the changed over? I just found that Matrix forum area; and see 2013 posts with the old style. Seems like it wasn't all that long ago. I still have a few more days to study up on this before the exam. I'll do my best. Thank you sir.

I have been trying to find more information about the SR-762 and found some forum discussions elsewhere dating back to 5+ years. Between all of those posts I compiled a list of what people said were compatible uppers for the real SR-762. Unfortunately I have no way to verify at the moment, but here is that list: Armalite AR10A, Larue Tactical, KAC (Knight's), LMT, Matrix Arms (they make the Ruger receivers), Genesis CNC. Does anyone else around here have a way to check any of these? Is that really true that an AR-10A upper fits on a SR-762? I found that listed more than once as being compatible, or maybe they only mean the distance between takedown lugs and hole size? I actually found a crappy blueprint JPEG for the AR-10 lower when I was researching my first AR-15 build. Unfortunately I don't know for sure what version it is or anything else about it. It is very low resolution, and cutoff at the bottom where that technical information would have been found. One of the few things I can make out in the details is that it says "Proprietary and Commercial". I found it again just now with a simple Google image search for "ar10 lower receiver blueprint"; it is currently the 22nd image, 1116 x 675 pixels. While trying to finish this post I found a few .pdf files which are much more complete with the same measurements; this time for something called a KAD-10. I assume I shouldn't be posting pictures that are copyrighted or whatever. After looking at comparison photos of AR-10A and AR-10B, I believe these prints are all for the AR-10A. Could this by why Ceratac says "it doesn't fit anything" and they won't release the measurements (because they are directly copying something proprietary)? Does anyone know if the 5d tactical jig is supposed to support the AR-10A layout, their website is very unclear? Should I be moving over to the 80% forum now or is this ok here? My kit still hasn't shipped, though I'm not shocked since I ordered some other things too, and it seems like everyone is swamped today after the holiday weekend. I'm still expecting to see it later this week since all my other orders with them showed up in two days flat. First order of business will be comparing the lower to these blueprints. Quite frankly I simply don't know what I don't know. I haven't laid hands on a 308 build, much less compared all the variations. I guess I'm just talking to myself in public now... But really; thanks for all the help so far.

Thanks! I found some pictures of a Matrix Aerospace SR-762 that appears to match the physical features shown in images of the Ceratac kit. No specific blueprints yet but I'm a lot less worried about that now. The pocket looks normal enough and I simply need to worry about placement of the FCG inside of it. From what I can tell, the only variations in position are based on the distance between the pivot pin, and the selector; both of which come "finished" in the 80% lower (selector location being indicated by the detent pin hole). I should be home free if all that is in fact true. I'll be sure to take my time with this and measure everything repeatedly before I get started.

I appreciate the vote of confidence on that method. While trying to find more information about it I stumbled across a page on the 5d tactical website in regards to their jig working with the Ceratac lower. They refer to the lower as a Cerro Forge - Ruger SR-762. I assume that means if I can find an SR-762 to measure against; that would actually allow me to do a real comparison with other 308 FCG layouts. I saw a measurement comparison between three different 308 platform "standards" in a recent thread on AR15.com while searching around. It was in reference to the reliability of 80% AR-10 builds. I don't see a reason to copy the image here since I don't know if any match up with the Ceratac kit. Still not sure exactly when my kit will show up given it is a holiday weekend. I will be sure to report back my findings when it does. In the mean time I'll see what else I can find out about this. I haven't found a review or mention of anyone else building this particular kit; should be interesting.

I thought I should throw my hat in the ring here. I had been eyeballing the Ceratac kit as well until I asked them about the machining. I have built their AR-15 kits without a jig; simply following blueprints. Unfortunately the response I got in regards to the 308 kit is that it's not like anything else, and they won't provide measurements. All that said; they have been on sale this weekend, so I ended up buying one anyway. I DID NOT buy their jig plates (Conversion Kit) since I don't have a 5d tactical jig to attach them to. My thought was that given it comes with their upper, I should be able to measure everything very carefully to determine where the FCG should be located. The trigger has to fit under the selector and be tight in Safe, and the hammer has to hit the firing pin. Doesn't seem like rocket science to me. Furthermore; the selector detent usually runs straight up into the center of the selector hole, and the other two pins locations are referenced off of that. I do have measurements/blueprints for DPMS and AR-10 lowers; but if what Ceratac says is really true they won't be too much help? Has anyone actually seen or built one of these? Are any of my suppositions totally off base about how the location of the FCG can be determined? I'm not entirely opposed to buying the conversion kit to get a helping hand if I really need it. But quite frankly, I think they should provide the measurements and don't want to encourage that kind of behavior on their part. Is there really a concern that some other manufacturer is going to copy the design, or did they copy something they didn't have permission for? Any insights or further discussion would be appreciated. I honestly didn't even think to ask what type of magazines were compatible so I'll have to get in touch with them again later this week.