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NonEx posted a topic in Technical DiscussionSo... I recently purchased two WE M4 GBBR receiver kits from KY Airsoft. Two blank uppers and two lowers, one with Colt markings and the other with Daniels Defense ones. Looked super nice, tight fit and the pin holes on both, just looking at the blank kits (upper and lower, switching them around) seemed to line up between the two kits. Which is great because I got the two uppers to have for my dual upper URGI build project. Basically building the two URGI uppers with the two blank uppers on the Colt lower and having the Daniel Defense for something else in the future. BUT! When KY Airsoft re-finished (i.e. new "paint") the receiver kits they did not re-finish the receiver pin holes, making them undersized by about 0.3-0.5mm So, when I went to install the parts and pins in the new kit, they did not fit. The receiver pins are 6.29mm in size (using RS DPMS pins. Have worked on previous WE M4 GBBR rifles that were complete and came with WE OEM pins installed). The receiver holes were something like 5.95mm-6.15mm in size. At first I put the receiver pair I was working on together, made sure they were a tight fit and the holes lined up and went to work with some 400 grit sandpaper wrapped around a 5.5mm punch to get the size right. After an hour of working the punch/sandpaper in the holes and the pins still not fitting I got frustrated and moved on to some more aggressive methods... 😐 Busted out my $20 USD hand-help cord-less drill and went to town with a 6.5mm metric bit. Needless to say, it did not go well. Firstly because the bit is too big, secondly because I did it hand-held with a $20 USD cordless drill, and I did not clamp the receiver kit in place so when the drill bit bit into the aluminum receiver it jerked around and I ended up with some pretty wonky holes... Anyways. Doing some thinking and math I would assume the receiver pin holes should be 1/4" in size, which equals 6.35mm. Meaning the pins will fit but not have a lot of play in them. My question is, and what I need help with is. How in the h*ll would I go about re-sizing the receiver holes to the proper dimensions, keeping them centered and aligned, without jitter when drilling, AND doing this consistently on two receiver kits so that they would be interchangeable when finished? Sounds like an impossible task without a solid jigg, a super sturdy and precise drill press or with a CNC router or something. So, I would like to know what your thoughts and ideas on this are, and what I can do to get this right on the receiver kit that I haven't messed up, and the new kit I bought to replace the one I damaged 😛 BTW, I have tried making this dual upper dream become reality once before by just buying a stand-alone upper (years ago, not from KY) to swap with my existing old WE M4 GBBR kit. On that upper that I got the holes weren't even in the right place to go with my existing lower so... Maybe I am chasing the impossible here? HALP, my OCD is killing me 😢 Maybe one of my Swedish buddies can help? @MODDAN @GRIM! @Dj_komodo