Re-sizing and aligning WE M4 GBBR receiver pin holes - HELP!

[NonEx]

So... 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

[Katotaka]

IDK.... 80% jig? even with that I won't be too sure

maybe a manual mill equipped with DRO, but that could still be PITA to work with

[Rob15]

Using a hand reamer would be your best and easiest bet I think, it'll follow the existing holes and just clean out any excess paint and a small amount of excess metal.

Only issue is that you've already had a go at the holes on one so they probably aren't quite so aligned anymore, in which case it'd be a machine job to get them aligned again.

[Dj_komodo]

I had exactly the same problem with 2 of my newer lower receivers... I used a round/half round needle file to make the holes larger, took me about 1 hour per receiver.

Im maybe lucky or gifted but it worked 

But you have to do a lot more work if the holes on the upper are smaller...

[NonEx]

Dang... Not looking to promising so far 😐 

Rob15, can you link to a picture/page of a hand reamer? Not sure I am familiar with that tool. just so I know what you mean. The one I messed up is scrap in my opinion already so no rescue operation on that one 😛 

EDIT: Like this?  Seems promising. But what do you think the odds are of doing that process by hand with that tool on two separate kits and having them mix and match?

 

 

DJ, yep, both upper and lower holes are undersized. Lower is manageable due to the thin walls and very little material to get through, but the uppers, working through that block of aluminum and keeping things aligned and the rights size... fuuuu 😐 

BTW, were yours WE OEM lowers?

I am starting to wonder if I need to turn to the dark side and buy RA Tech forged recievers and ask them to make sure the holes are in spec. lol #FML

[hitmanNo2]

The receiver you've messed up might still be usable with one of those magic pins or whatever they're called.  The ones that kind of twist and shift to fill a loose tolerance.  I've not used one before so no idea how good they are though.

[NonEx]

Actually have one but from what I have seen they are for the front pivot pin hole only. That one is actually a pretty good fit still, but the rear pin hole, not so much  

[Dj_komodo]

3 hours ago, NonEx said:

Dang... Not looking to promising so far 😐 

Rob15, can you link to a picture/page of a hand reamer? Not sure I am familiar with that tool. just so I know what you mean. The one I messed up is scrap in my opinion already so no rescue operation on that one 😛 

EDIT: Like this?  Seems promising. But what do you think the odds are of doing that process by hand with that tool on two separate kits and having them mix and match?

 

 

DJ, yep, both upper and lower holes are undersized. Lower is manageable due to the thin walls and very little material to get through, but the uppers, working through that block of aluminum and keeping things aligned and the rights size... fuuuu 😐 

BTW, were yours WE OEM lowers?

I am starting to wonder if I need to turn to the dark side and buy RA Tech forged recievers and ask them to make sure the holes are in spec. lol #FML

No clue, bought 2 from AsiaAirsoft years ago (LVOA & Colt trades)

 

How about making the pins thinner? lol

put one end in a drilling machine and make it spin while holding it with sandpaper

[NonEx]

Thought about that but then I have off-spec pins and still got bad receivers 😛

Might be easier, but again getting a consistent shape and size on a spinning pin with sandpaper is probably also difficult. Guess it's cheaper to experiment with though. But hmmm, naah, don't like it 😐 

 

Right now the hand reamer tip is looking pretty appealing  

[renegadecow]

I just go with super glue + metal filings if the hole is too big. If it's too small, sand paper around a drill bit (smooth end) and a LOT of time and patience.

[Brigg]

When I need to ream out holes, I just use a drill bit tightened into a thread tap handle. The hole size you need is 1/4", which is the size of both real steal and WE takedown pins. Probably easier to source a drill bit that way then trying to find something in metric.

[icolater]

Hey Nonex

Iv had about 10 AR receivers Cerakoted and as mention above a needle file is needed to remove paint build up in the pin holes. It’s only paint you are removing so it shouldn’t take to long.

TBH I would just buy a new receiver, the effort involved in fixing the damaged wouldn’t be worth it. No matter what you do it’s always going to look funny. 

If I was to attempt it though, I would use that putty that turns to metal after a while, sand down the area, re drill the holes, then get it refinished.