WE "Open Bolt" parts in AWSS-Specific Receiver

[Katotaka]

First of all, please don't hate me.

 

I was given a set of CNC'd WE M4 receiver set in Magpul flavor, yes, the billet style one and seems it's made by Prime AFAIK. The set was collecting dust for few years and I've recently decided to give a face-lift to my WE M4.

 

The lower seems it will fit fine as I see it bcoz the lower parts didn't change at all for the years, but the open-bolt bolt carrier seems too big to put inside the upper. I searched my old parts bin and found that the old BCG has slimmer diameter except the rear end, which the upper has a bigger space to fit, while the new BGC has uniform diameter along the length.

 

I have "some" access to machinery so this is what I am thinking:

 

a) Mount the open-bolt BGC on a lathe and reduce the diameter, sounds as much crazy as "doability", cause option B is just ridiculous.......... wait for it.......!!

 

Old upper inner dia. measures 1" / 25.4mm; old BCG rear 24mm front 23.2mm; New BCG 24.2mm.

 

What I plan to do is mimic the old BCG by reducing 1mm diameter, sounds crazy but 0.5mm radius is promising...

 

 

Enlarge the inner diameter of the said upper to 1 inch, acquire a 1 inch drill bit / end mill and *fruitcage* the hell out of it. The tricky part is finding such tool and I don't have access to machinery of that size.

I imagine the cost of doing so is greater than just switching to another system, where I could just built AWSS system in the receiver and leave it as a *fruitcage* beautiful wall hanger.

 

BTW I am thinking if I do the switch I will just get a WOC40 and add a Svoboda AAC .300 kit.

 

 

 

*Doodle styled technical drawings coming soon to help the interested guys understand my struggle...

 

** Edit: typo

[renegadecow]

I say caveman it. People have port and polished engine cylinders with less tools. If you can find a long enough shaft, something to increase its diameter like tape, sand paper and a drill I think you can whittle down the receiver in an hour. Could just be that one receiver too as you can convert closed to open bolt on the standard receivers with the BCG dropping in plus adding that collar spacer where the barrel nut goes.

[jkpics]

If you are doing it do it around a RA-Tech steel BCG.

[Katotaka]

I say caveman it. People have port and polished engine cylinders with less tools. If you can find a long enough shaft, something to increase its diameter like tape, sand paper and a drill I think you can whittle down the receiver in an hour. Could just be that one receiver too as you can convert closed to open bolt on the standard receivers with the BCG dropping in plus adding that collar spacer where the barrel nut goes.

 

The machinist in my workplace says lathing the BGC is doable, before harming the upper I would try BGC route first.

 

 

If you are doing it do it around a RA-Tech steel BCG.

 

As a ordinary guy who hasn't really trained operating such machinery, I'm going to do with original aluminum BGC.

Sometimes lathing brass or POM rods scares the hell out of me

 

Anyway the OB conversion kit still readily available here in HK, if I fail I can get one, besides of the complete BCG, which also comes with extra trigger box, hop chamber w/ inner barrel, magazine lip and bolt stop.

[Bucko]

If you ever want to just get rid of the receivers, I'll be right here.  

In the meantime, Try using an RA Tech steel BCG.  Maybe take the receiver to a store and ask them to let you test fit it.  Better to try that first than start messing with things and find out later you didn't need to.

[Katotaka]

Judging by pictures I don't think RAT BG would fit, because the Prime upper has a bump / thicker wall starts from around 20mm measured from the rear end.

 

BTW I would try not to alter the upper if possible, except drilling a 3mm hole for the anti-rotation pin of the NSR rail.

[Katotaka]

Lunch break just passed, I lathed part of the BCG and I found that there is a part protruding from the BCG body i.e. BCG profile not totally round, I needed to skip the involved part and dremel it later...

 

Apart from the above I think I will be using that bcg on my final build, wish me luck.

[Katotaka]

Update:

 

Yesterday my boss leave early and I have my computer doing some batch process...... so I decided to take my advantage, the machinist was doing some other work, the lathe was free and I was allowed to use it.

 

I worked along the length of the BCG but my measurement on the lathe seemed off, OD of BCG end up something like 23.7mm but it fits inside the upper, as I said I had to skip the part where the dummy gas key is mounted to, I switched to a grind wheel and remove some more material and touch up smaller parts with a dremel.

 

After all I can fit whole BCG into the new (old?) upper but still need to file down the side nozzle guide, with the thinner BCG the side nozzle guide is now protruded like 0.5mm from the surface, which is pressing against the inner surface of the upper.

 

 

To do:

 

1) File down side nozzle guide, maybe getting a set of RAT one and mod it to compensate the strength of reduced thickness.

2) Transfer upper parts from OEM upper to Prime upper.

[Katotaka]

Update: The upper in question is pretty much done, what's left to do are trying to fit a PTW raptor charging handle and blacken the BCG.

Here comes the pics...



Current state of the said BCG, the silver-ish color is bare metal.



Compared to old "AWSS" BCG, what I've done is put the current BCG on a lathe to copy the dimensions of the old one.



Since the "open-bolt" BCG is not entirely cylindrical, I have to skip the part ( highlighted ) where the dummy gas key is attached to, I dremeled that part, hand filed then sand paper'd to mimic the machine mark.



Left side, I thinned the nozzle guide/stopper with dremel to match the BCG outer diameter.

The brownish color is where I test the blackening chemical, seems not durable enough.



Fitted inside upper, I'm quite happy with the tight spacing, feels less wobble than my old G17 slide/frame.



Bottom, very very few space left between upper and BCG, while still able to move kind of smoothly.
When bolt is closed and I pulled the BCG halfway, the nozzle is "sucked" by chamber packing and it can pull itself back by the nozzle spring even against gravity.

The uneven part is where I used the dremel.


The part in the upper where its inner diameter become smaller, which is different from original WE upper.

 

Tested firing on an old lower and works OK, time to gather parts to finish the project.