Time to put them thinking caps on...

[e-luder]

Hi Folks!

So...

Everytime a Tokyo Marui 5-7 comes across my table, I get the same request: "Can you make sure that you re-inforce hop unit so it doesn't break?'

or they don't even have to ask. I'll just do it.

And everytime, I come up with different ways to do it.

So, I recently came upon an idea. I was hoping that any gun tech/pistol smith/physics majors/Auto-CAD majors/and whoever else majors come forward and chime in.

First, let me set us up the bomb first:

So the Marui 5-7 has always been problematic in their upper assembly. From slides to cracking, to BBUs breaking to hop units breaking.

THe issue that i want to explore is the hop up/outerbarrel issue wherein, either the hop unit breaks or the outer barrel breaks (or both).

Unlike the majority of pistols out there to date, the Marui 5-7 is unique in that the hop-up unit, outerbarrel and recoil system is one piece (to put it simply) whereas some pistols like a Glock or P226 or the sexy new HK45 has seperate parts: the hop up unit/inner barrel assembly and an outer barrel with a chamber to cover and hide the hop unit with a separate recoil spring assembly.

The set up for the 5-7 components are fairly simple. The hop unit basically clamps the outerbarrel into place. The outer barrel is held in place by two locking lugs. One on each half of the hop up unit. There are two holes where these lugs go into to lock the barrel in place. A recoil spring sits around the outer barrel and has a spring stopper and o-ring at the end to prevent the recoil spring from shooting out of the gun on the muzzle side.

This is how the whole mechanism looks like:


What eventually ends up happenning is that either the locking lugs or the holes on the outer barrel sheer right off. Or both. Thus, the outer barrel will just come out of the gun on the muzzle end since it's not fastened to anything.

Now, I've always JB Welded the outer barrel to hop up unit. I even went at as far as to try and weld the fuckers together. Of course that's resource heavy and I don't really want to call my welder guy each time one of these comes across my table. Not to mention the price to for the whole repair in general.

Everyone has their own fix for this issue.

Here's what I want to run by you:

If we analyze the structure of this whole system, we soon discover that there is something yanking the outer barrel. Logically, for a the lugs to break, there must be some sort of force coming (or going) to destroy it.

My theory is that the return stroke of the slide is this force.

Because of how the barrel and spring stopper is placed on the outer barrel, i figure that the repeated blows eventually destroy either/or the two components.

In that sense, what if we "float" the barrel? That is, let's get rid of anything that has the potential of absorbing the force (on the barrel only) and let's disperse the kinetic energy in the slide itself.

This means the the spring stopper will have to be moved to the opposite end (where the hop up unit is) and put recoil spring on top of it. Then let's let the recoil spring itself rest on the slide.

Like this:


Well sort of. I forgot to put the spring stopper in there.

Here's a comparison:
The top one is the modified one.



This will "float" the outer barrel and the recoil power is offset to the slide.
Of course the slide itself will require re-inforcement (ie. install and JB Weld the Creation aluminum inner slide).

So my question is from a purely empirical and practical point of view:

From one pistol smith asking another, will this work? Will this preserve the outer barrel AND hop up unit??

Given the frailty of the Marui 5-7 I can't put one through its paces and see if it does break. On top of that, parts a kinda hard to find sometimes. I don't wanna be SOL since the guns are with only for repairs. They're not mine.

What you think?

[e-luder]

... A better question is:

Would do you think will happen with this set up???

[e-luder]

I forgot...

the whole idea is to stop the recoil spring and spring stopper from yanking on the barrel. This occurs when the spring stopper comes into contact with the o-ring resting on the end of the outerbarrel.

I say move the spring stopper to the hop up end because i want the spring to completely out of the hop up unit....

[ThunderCactus]

Too late to think, but you could solder the barrel to the hop unit, given you abrade off any coatings and apply flux. It would be just like soldering a copper pipe together.

[e-luder]

Originally Posted by ThunderCactus

Too late to think, but you could solder the barrel to the hop unit, given you abrade off any coatings and apply flux. It would be just like soldering a copper pipe together.

Hmmm....

That's probably the smarter and almost surefire way of preservation.

But I need the modification to be NOT permanent so that the operator can break everything down whenever he/she feels necessary. I;m trying to think user friendly here (for lack of a better term)...

[ThunderCactus]

My next question is, why wouldn't they design it like you modded it in the first place? With the recoil spring on the slide instead of the barrel?
Seems like the obvious way to fix it, by floating the barrel like every other pistol out there.
What if you used a thin steel washer to prevent the spring from tearing up the slide and spread force a bit?

[grantmac]

I second the use of a washer to reinforce the end of the slide.

-Grant

[e-luder]

Originally Posted by ThunderCactus

My next question is, why wouldn't they design it like you modded it in the first place? With the recoil spring on the slide instead of the barrel?
Seems like the obvious way to fix it, by floating the barrel like every other pistol out there.
What if you used a thin steel washer to prevent the spring from tearing up the slide and spread force a bit?

For realism's sake, I guess.
The real FN5-7 has the same system almost.

Difference with them is that there's no hop up to fuck with and house inside the chamber. lol. So I think the barrel/chamber is one pice.

Keep in mind though, Marui guns are not intended for propane. But most operators in the West use propane as a power source anyways. Might've pass TM's QA tests with duster but I guess they didn't test with other power outlets..

Anyways, i think the slide is fine. I'm just curious to see what other people think will happen to the outer barrel and hop up unit with this kind set up.

Any other wanna chime in?

If the OP is unclear in any way, just let me know and I'll clarify further....

[MaybeStopCalling]

Originally Posted by e-luder

Hmmm....

That's probably the smarter and almost surefire way of preservation.

But I need the modification to be NOT permanent so that the operator can break everything down whenever he/she feels necessary. I;m trying to think user friendly here (for lack of a better term)...

How bout tapping the hopup and barrel for a pair of set screws? Reinforces the two and is still removable.

[siggypoo]

I'd be concerned about that sort of mod introducing new stress points to the setup. New holes that could cause cracks, and eventually breaks.
I don't know the gun myself. Is the barrel and hop up area, where they come together, round? If so, what about threading them together? Even a single wrap of plumber's tape would create a tighter fit while adding a modicum of shock relief. Same if a bayonet mount (a-la SLR camera lenses) was employed if the barrel and hopup cannot be screwed together.
It'd be great if I could find a manual and parts diagram online, Bueno manual databases seem to have had users bother to scan the damned thing.

Or am I completely out of my depth here, lol?


Location: YYZ VOR 062 radial, 17.5 DME FL5280

[ThunderCactus]

If the lugs are breaking, threaded holes are guaranteed to break

[e-luder]

This is how the whole thing looks like WITH MY MODIFICATION:


This is inside the hop unit UNMODDED:


These are two things that break when UNMODDED:






THe stock set up has the recoil spring rest on a metal piece and o-ring at the end of the BARREL. That metal piece then rests on the slide.

Sooooo if we analyze this set up, my way of preserving these parts would be to let the recoil spring rest on the bare slide. I don't know what will happen since the spring stopper rests on the slide anyways...

So again, my question is based on theory and I want to specifically know what you guys think will happen to these fragile parts if i go run with my set up.

Will the barrel break? Will the hop up stay intact? or am I just wasting my efforts?

The modifications mentioned above are useful for Steel barrel and stock barrels out of the box brand new. But are moot once the barrel breaks. Believe me I tried tapping the hop up.

Plus, there's a gap between the hop unit and the outer barrel so that the recoil spring can fit in there. But I usually JB WELD that space to keep the recoil out of the hop unit.

It's very resource heavy as well and drives the repair bill up.
...which people are not too keen about. lol.

So again, what do you think will happen if we "float" the barrel?
This means the recoil spring rest on the slide itself (not on the spring stopper located on the muzzle end of the barrel)...

Im curious to know what you guys think.

[lurkingknight]

only a redesign of the outer barrel and hopup unit is going to eliminate this issue. The materials used and or the method of the merge between hop up and outer barrel is weak.

The barrel moves backwards and forwards on that lug due to the blowback movement and the forces exerted on the barrel during the blowback.


even on duster there are complaints in japan about these 3 ploblem areas, (front of the slide, outer barrel and hop up) The difference is they don't care as much since they have access to the factory parts service. The replacement parts are about 30 bucks total and the pistol itself can be purchased NEW for around 120-150$

There's no reason to redesign it or make it out of any better materials when replacements are so cheap.


The hop up and outer barrel need to be redesigned, both made out of steel. The hop up instead of having the pegs needs be tapped and threaded. The outer barrel needs to thread and screw into the hop up, only then are you going to get the surface area to spread that kind of load. Steel might be overdoing it, aluminum could probably handle it, but it's soft. You can cut aluminum with an xacto knife if you want. It's not exactly a great metal to hammer at constantly.

[e-luder]

I was hoping you'd chime in LK.

I agree that it requires stronger material but given what we have and how old the gun is, I don't think that scenario will happen. So the West is SOL and are forced to "re-design" the system themselves.

As you said:

There's no reason to redesign it or make it out of any better materials when replacements are so cheap.

So what if the load was offloaded to the slide? Let the spring rest on the slide instead of the barrel spring stopper thing??

[lurkingknight]

I don't think the slide itself could take the entire recoil shot. If it was solid metal, sure, but they wanted to sleeve it with plastic like the real one, so it halved the thicknesses pretty much of both materials. That's why you get the front of the slide cracking at the weld.

I don't think the creation slide does much for the plastic outer slide, renegadecow on asm/asf/arnies also ran this and his slide still cracked.

I have packed the spaces between the 2 pieces on my 5-7 with rtv silicone and have not seen an issue here yet. I have a feeling the creation slide and the rtv mod will move the stress points around. The inner portion of the slide is the front end which the creation slide can replace, but it butts up against the BBU and the rest of the guts housed in the slide. The guts float inside the slide and are tension clipped in by the outer slide. The front and inner halves are only merged by 2 tiny screws (might only be 1) just under the ejection port. I think the BBU might be anchored through the outer by the rear sight, but even then there's not a whole lot that weld the inner and outer slides together. But after 2 seasons of use, I have not had any parts of the slide or BBU fail.

I have however gone through a hop up unit already. both lugs sheared off, even with extensive rtv to merge the outer barrel into the hop up.

There was an effort by someone to 3d scan the hop up unit and try and get out there for people to play with, but I have not heard of any progress on that front. Ideally you'd cast it in steel or have it CNCed but to achieve that it may need a redesign as the precision around the lugs might not work.

The other option in terms of a redesign is that you would somehow split the hopup differently or include a portion of an outer barrel that extends out from it, then you thread the outer barrel on, but that would need to be a full kit.