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WE Gas Blow Back M4A1 Carbine

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Heres my latest custom job, a WE GBBR version of a Colt Slab Sides Carbine. If anyone knows a pla ce that could machine me a proper outer barrel, I would like to get in contact with them and have a pr

Heres my custom WE M733. I have a modified RS Bushmaster upper receiver as well as RS buffer tube, castle nut, stock, stock plate, pistol grip, front grips, front sight, and some various other small b

Hehehe, Im with you Hwagan. I dumped my LM4 like a bad habit a few months ago and switched back to the WE platform. Used the extra money to get myself a trademarked M16, slapped a RS A2 upper receiver

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Because of the way the system works the o-ring (part #122) would have to leave the brass cylinder. All of the gas that pushes the bolt carrier back against the recoil spring needs to be released. I'm pretty sure it was briefly discussed a long time ago.


You might be able to get away with having several large holes drilled into the very end of the cylinder, but even then it might not work, and if it did probably not as well. The way it is now is how almost all modern GBBs work, and it honestly is a very good system. Otto's suggestion of polishing the outer lip of the cylinder and Loctiting the screw that holds the nozzle/piston head assembly down is perfectly sufficient to keep things working for a very long time. :)

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For those of you in HK that do not have camping stores you should be able to find propane in shops that supply plumbers. Propane is used in torches to cut pipes.


Propane is safer to use and transport (at least in the UK) as the presure is the same as green gas at 175psi @ 100 degrees F but propane is kept in regulated bottle types where green is in aerosol cans.


Also, the gas chromatography and mass-spec analysis of green v's propane is identical as can be seen at the bottom of this page;



The slight differences in the gas chromatography peaks is due to the added silicone.

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Chris, I hear what you're saying. It had occurred to me that because of the need to vent the blow back gas that the cylinder would need to leave the brass part.


But that gas should vent pretty quickly, and the force of the recoil spring should be sufficient to push the bolt back even after a short period of venting. So a couple or three holes around the rear end of the brass cylinder 'should' be sufficient. Relative pressures do equalize pretty sharpish if given the chance.


Failing that, looking at the other end of the problem......


why not make the base end of part 38 the same size as the hole it fits in. In effect making part 38 and the new stabilizer piece as a one part unit.


So the enlarged base of part 38 would alleviate any sideways movement. You could also fit a larger bolt to the rear end to secure it on the bolt carrier. Obviously the bolt part will be dependent on any clearance issues behind it.


Obviously I understand the manufacturing implications behind this, so it might not be financially viable to do such a thing.


There is a very big trade off between the best solution and the most cost effective.





Ooooohhh.... just seen that update WETTI.


I like the thinking, hopefully the frontal metal lip will help guide the rod back into place saving the seal in the process.


Playing devils advocate here (It's a habit of mine, I used to build sportscars and you have to see these problems before you build the thing), with this new part. Say the part 38 is allowed to become loose and flop around (which is the current issue). The force of the recoil spring pushing that extra metal lip back against the brass part 112 deforming it in the process. So it may cause further problems (not least an instant Jam). It may not, only time will tell. Any deformation of the relatively soft brass will still be enough to damage the seal.


The way to alleviate this would be to have the face of this new part more conical (enough to allow sufficient venting, but maybe big enough to keep it within the brass tube), so it guides back into the brass tube rather than trusting it to fate.


I'd draw a picture if I could use Paintshop.... (if I had a copy of Paintshop...)

Edited by The Chef
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WETTIl, thanks for the image. That seems to be an improvement. Would that new design affect the brass cylinder, though? No doubt the CNC steel ring will prevent the O-ring from shredding, but will it damage the brass cylinder if its mis-aligned?


I believe it's aluminum...


I really do not have very much info. on this...I was presented with the prototype for a brief comment, then this pic later on; that's all I've got at the moment.


Pls just wait for my friends over at TS One to officially introduce this thing, alright? I'm as eager as you to try one in my personal piece.... :rifle:

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hmmm, brushes up on his knowledge of specific metal hardnesses....


I think Aluminium is still harder than brass, but not by much, but that would still transfer any damage to the brass part.


not wanting to be the harbinger of doom here, but doesn't this look like a direct approach to solving the issue of 'the O Ring being shredded' rather than the issue of 'why is the O Ring being shredded'?


In this case, the cause is the opposite end of the physical problem. Stop the Flop (no viagra jokes here please...) and stop the O Ring shredding.

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Alright.. Got some reply on GGI.. Seems if the o-ring is not used there might be tilt on the outer barrel. But I am not sure why. Might be that the barrel and upper don`t fit 100% and that the o-ring help it get aligned.


A bit strange method to get something straight.

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Net Ronin, thanks for the pics. You know how its shaped like a cylinder, with the 2 sides shaved off say the have straight walls? Where are the straight edges? Did you install them facing east/west in the bolt carrier or north/south? Yeah this sounds kinda confusing...thought I'd ask anyways.

I put shaved off sides against the wall of the bolt carrier. Round sides will be top and at bottom of the bolt carrier. Sorry , I do not understand east/west term. Could you please explain how to figure which side is east/west/north/south if you do not mind?


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I put shaved off sides against the wall of the bolt carrier. Round sides will be top and at bottom of the bolt carrier. Sorry , I do not understand east/west term. Could you please explain how to figure which side is east/west/north/south if you do not mind?


Flat sides agains the walls of the bolt carrier. Gotcha! That's what I meant by east/west. You have the shaved sides in east/west orientation. If you had put the shaved sides facing top/bottom of bolt carrier, I would have called it north/south. I'm gonna have to tray it your way. I was under the impression that the rounded sides follow the side walls of the bolt carrier...except for me, it didn't work, about an inch away from the bottom.

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Just a note.


Talking to all my buddy's with REAL AR15's, they have told me a counterweighted buffer is exactly what you DONT want if more recoil is your desire.


It not only slows down the firing rate but DECREASES felt recoil.


Its done to smooth out the firing of short barrel AR15's and to control muzzle rise.


Needles to say the stock buffer is back in, gun runs like a champ with the stock one.





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