WETTI/AWSS - M4/SCAR/HK416 - Technical Summary Thread

[dirtdiver]

Originally Posted by Qlong

The UBR's receiver extension has a smaller different inner diameter than the stock WE, this will cause the top end of the bolt carrier to rub against the wall.

What brand of UBR was this?

Yup Qlong you're right the new buffer tube is slightly tighter causing the buffer to get stuck appx 1 inch from the complete forward position... The bolt carrier however seems to move freely. It is a UBR clone from Huang, Element i think. I am going to try to sand down the buffer head and then grease it. I think its only a matter of a mm or so.

@onemenace why would stretching the spring increase fps?

Thanks guys

[Ross]

If I put the open bolt we m14 precision (54 cm) inner barrel into my open bolt we scar, would the scar be able to shoot good? Or would there be not enough fps to project the bb out such a long barrel?

[Stealthee]

Originally Posted by johan_saint

Should can, if can not, you maybe need to custom the ring. I just built a M4 noveske using the M4 cqb 4th gen, the inner barrel connector is diffrent with other m4 gen, its more thin, so no need to custom the adaptor.

This is a confirmation that it fits without any modifications.

[johan_saint]

Originally Posted by Ross

If I put the open bolt we m14 precision (54 cm) inner barrel into my open bolt we scar, would the scar be able to shoot good? Or would there be not enough fps to project the bb out such a long barrel?

Whoaaa...that's the SCAR I want to built, between M4 and SCAR, I thinking to built a SCAR sniper, Because its more stable got many screws to hold the outer barrel and the brass tube housing...My friend is using WE G39C that should be the same hopup system for scar open bolt, now he using the nine ball hopup rubber for hicapa, even so the shoot is still average, and this is the art of GBBR, that the person must learn to skill to use a GBBR, not like AEG that the AEG is already skill to be use by any person. What you mean of not enough fps? As far as I know the longer the inner barrel, the higher fps will be.

[Ross]

Originally Posted by johan_saint

Whoaaa...that's the SCAR I want to built, between M4 and SCAR, I thinking to built a SCAR sniper, Because its more stable got many screws to hold the outer barrel and the brass tube housing...My friend is using WE G39C that should be the same hopup system for scar open bolt, now he using the nine ball hopup rubber for hicapa, even so the shoot is still average, and this is the art of GBBR, that the person must learn to skill to use a GBBR, not like AEG that the AEG is already skill to be use by any person. What you mean of not enough fps? As far as I know the longer the inner barrel, the higher fps will be.

Well I wouldn't even try this without first installing open bolt. Closed bolt is only good for cqb, as the accuracy is all over the place.

What I meant by fps is the barrel I'm using was meant for the m14. The we m14 shoots hotter than the we scar. I'm assuming a gun needs a little more pressure to take advantage of a longer barrel.

The inner barrel I want to get is almost 2 feet long. And a longer barrel doesn't mean more fps. It just means you get smaller groupings. A tighter barrel is supposed to increase your fps as it will get better compression.

But this is aeg talk. Aegs have something gbbrs will never have, and that's consistency. Fps of an aeg remains somewhat the same but on a gbbr it fluctuates anywhere from 5 - 50 fps. I guess I'll just put the barrel on and see what happens. lol

[m102404]

The negative pressure gas system doesn't work on a fixed amount of gas per shot...it's entirely dependant on the weight of the BB and the length of the inner barrel.

(ref. there's a very good little write up on Redwolf's site somewhere about how NP and PP systems work...diagrams and all)

Basically...there's two halves to the firing cycle so far as gas is concerned. Part1 - Firing...and Part 2 - Recoiling.

Part 1 is where the knocker knocks the mags main valve and gas is released up into the nozzle (open bolt or not). The gas is forced forwards since there is less pressure ahead of the BB (the atmostphere) vs. behind it in the bolt (open or not). Since the knocker is only retracted when the bolt racks back, it will stay forward and gas will continue to flow behind the BB as it travels down the barrel.

As soon as the BB exits the barrel there is now more pressure behind the float valve in the nozzle (open bolt or not) vs. in front of it. So the float valve is pressed forward, plugging the nozzle and pressure builds behind it in the brass tube/nozzle body. That starts Part 2.

Part 2
The gas expanding in the sealed spaced builds pressures and eventually overcomes the recoil spring of the bolt...the bolt travels rearward...the hammer is cocked on the way back and somewhere during it's travel it trips the knocker release (part #66 in the M4). The knocker retracts....gas from the mag is cut off....the bolt continues to recoil by remaining pressure and momentum. Bolt carrier bottoms out....and is slung forward by the bolt spring.

So.......with a NP system it will fire a BB out no matter how long the inner barrel is. It could be 1cm....or 1m long...doesn't matter. Gas will flow in/down the barrel until the BB leaves the muzzle. Obviously this will use up more gas per shot and you'll typically get very high muzzle velocities.

[Amos]

Originally Posted by Ross

The inner barrel I want to get is almost 2 feet long. And a longer barrel doesn't mean more fps. It just means you get smaller groupings. A tighter barrel is supposed to increase your fps as it will get better compression.

You're a little confused there Ross!

Longer barrel DOES mean more FPS.

More FPS DOESN'T mean more range and accuracy

[Ross]

Good to know guys. Thanks for the corrections.

[SONNY BLUE]

Hey! guys, A friend just got a WE M4 CQBR GBB from a local retailer and he fired a couple of rounds in the store and it works fine. When he got home and tried it with a fresh mag, He had trouble pulling the charging handle back. He tried to hold the bolt(using bolt catch) back before inserting the mag and then releasing the bolt, it went back but still could not pull the charging handle back again after.

This question might already in one of the pages here but I might have missed it. Any suggestion/s? before going back to the store. Thanks!

[Ross]

gun on safe?

[ShelledPants]

Gun lubed?

[SONNY BLUE]

It's on Semi and yes, it's lubed. Everything works well without a mag. Switched lower receiver and bolt carrier from another rifle, same results. Retailer advised to bring it back to her store and she will check it out but will replace the rifle anyway. Thanks Guys.

[ACCL]

Hey guys I found this kit on rosv ( http://new.rsov.com/product.php?lang...471&cateId=146 ) and was wondering if I can ship this in?

[Wrath144]

Why does my guide rod spacer, the clear plastic one, keep getting smashed up? I've had two broken so far, and without it the rifle just vents.

[m102404]

The spacer holds the nozzle forward when the bolt is forward in position. As you've seen, without it the nozzle will just let the gas blow back and mess up the cycling.

If it's too long, it will stress the nozzle (as the bolt carrier slams forward)...or fail.

If it's getting smushed/split...it's too long.