AR drill/mill fixtures... have we been doing it wrong for years???

Well something to keep in mind.... I made my own side plates and a grip block like you did... got 3 RTB AR15 blanks and that other ar10 replacement to do... as I don't have any stripped lowers laying around I used an ar10 lower from another supplier out of oregon to mark where to drill the grip screw hole.. just dropped a layout punch through the grip screw hole a light tap.. figured better to be sure dead on in right spot etc.. drilled it and used end mill to counter sink outside etc.... went to test it on onea the RTB AR15 lowers and... the hole is off.. by about a 1/16th or better..... tried to figure it out... then put the block on the RTB AR10 blank... lines up almost perfect grip boss is thicker on the RTBAR10 so gotta widen the slot a lil etc.. then put it on yet another AR10 lower this one from 5D and it lines up perfect! put it on the one from oregon and again lines up perfect... it seems that not every 80% company actually has the grip screw in a universal location/angle still yet to be determined as have ALOT going on right now will try to get pics time permiting... just a heads up it might not be so universal... gonn slot the grip screw hole so can get it to work with the RTB AR15 lowers later

Slotting it probably isn't a bad idea, though at this point I wouldn't use the dimensions of any of RTB's lowers as a reference point. Look at it this way, If you have to move the grip screw hole in the jig to get it to work, then you will also have to move the hole in any grip you want to use on that lower too.

I've been able to check my little jig against a number of AR lowers at this point. A mix of commercial ones (Anderson, Compass Lake, and Rock River) as well as 80% ones from Brownells, Midway, and Tactical Machining. The only ones I have with issues are the two that came from Right To Bare.

So, from my point of view, I'm just going to assume that if the dimensions of a RTB lower doesn't fit the jig, it's the RTB lower that is wrong. That's just what my small sample size of lowers is showing me... whoever machined RTB's lowers can't read the long published blueprints for an AR. ;)
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yea I needa pull a few apart and check it against them..... noticed they have the 308s back on the site so I guess whoever is doing their lowers got the detent hole corrected... just been so busy latelly haven't had alot of time to just put into the shop...