Wiring a G&P Crane stock & batt - a proper job

[Tommygunn]

Well I recently got sick of having a PEQ batt box on the front of my M4 and really wanted a more streamlined look i.e. Crane stock. Since I like things to be as real as possible my only choice of Crane stock was going to be a G&P unit that uses 17mm AF cells.(This guide can be applied to stocks that use SubC cells e.g. CA, Star etc)

First things first I stripped my M4 down. Then I proceeded with the Dremel and a disc cutter to chop out the section of lower receiver shown below. It involved doing two parallel cuts length wise, snapping the 'tab' out of the receiver with a pair of plyers and neatening up the jagged edge with a milling bit.

 

The same was repeated to the rear of the receiver tube but not quite the same length.

 

I then chopped a chunk out of the stock tube bolt washer to allow the wires to pass by it. Again multiple disc cuts and milling/hand filing to tidy it up.

 

Next it was on to making the wire and where one of my little innovations comes into play(I thought of it first - Hurricane stole my idea!).

Basically the wire is measured up and sheathed in heat shrink. It is then wrapped around a pen, in a compressed state, with enough coils to allow it to extend to the furthest position of the stock plus to allow the stock to be removed for batt change. Take you time with this.

 

Then blast it with a hairdryer and you should end up with something similar to this:

 

Here's how it looks when fitted in the receiver:

 

and from inside:

 

and looking down the stock tube:

It is important to note that you need assemble the stock tube, wire and bolt/washer first before mating it to the receiver tube/spigot. This is because if you were to drop the bolt and washer in last, after mounting the stock tube and wire, you would not be able to get the washer past the coils, at least not without a great deal of yelling and shouting.

[Tommygunn]

Now I opted to use some AF cells I already had so I sourced the battery mounting bracket(three point plastic thingies) and proceeded to build my own packs.

As you can see from the photos below, I have used Corally plugs that connect from the rear. This is for four reasons; they are compact, high quality/low resistance, allows for easy access and prevent the plugs from separating from the battery when the stock is extended.

 

 

 

 

Here we have the Corally 'male' plugs into which I have drilled a hole for the wire.

This just the allows the wire to have have less twists and turn and generally be more ergonomic. The size of the hole also allows the wire sheathing to be supported and since it is silicone wire it will not melt when soldering.

[Tommygunn]

Prior to assembly, the pics below demonstrate how the coily wire looks in relation to the battery pack. As you can see the coils sit in front of the centre cells and if needed the cells can give the coils a push to help compress them.

You can also see how well the plugs connect to the sockets on the battery pack:

 

Next was the job of attacking the stock tube to allow the battery bracket to fit when the stock is slid forwards. I basically used the same method as before making lengthwise cuts to the correct length, snapping the rectangle out and then neatening with a milling bit and hand file:

[Tommygunn]

Below are some pics of how the battery looks when seated in the stock tube. You have about 1cm of space in the back end of the Crane stock so you don't have to worry about any plug or battery overhand.

 

A look from the rear:

 

In this pic you can see how the wire goes with the battery and stock tube:

Depending on the gauge of your wire you may have to do some more Dremeling to the stock tube where the wire is sandwiched between the battery and stock tube as it can be a tight fit and prohibit the slide from going fully forward.

 

In the following pic you can see how I re-wired the gearbox but still utilising the front wiring, which was used for the PEQ and the fuse. Incidentally, I will still be able to use a peq battery by simply making a double ended socket and connecting the two rear plugs together. As it stands the double plug is used at the front to make the circuit:

You can see I've put in some slack in the wire between the gearbox and stock tube to allow the gearbox to be removed from the receiver.

This excess can be coiled up in the cavity behind the gearbox as shown here:

 

After all that you get this - nice and neat and no wire snags .

 

It is advisable that when installing the battery that you drop it into the stock tube first and connect it. Then slide the stock over the battery(without storage caps installed) until it is as far forward as it will go. Then extend the stock and detach it slightly so you can put into place the storage tube caps and then replace the stock. This is where the extendable length of the wire is critical since if it is too short you will not be able to un-hook the stock from the stock tube.

Do the reverse the charge/remove and it may be advisable to attach a ribbon or cord to the battery bracket to allow removal because the battery can be tight in the stock. Otherwise you can remove the butt pad and use a screwdriver or stick through the back end to push the battery pack forward to enable removal, once the caps are removed.

 

Any questions then feel free to ask.

[Catman]

Nice work!

[Tommygunn]

Thanks.

[BARsrule2]

Awesome! Any hints to where you sourced the plastic cell holder thing?

[Tommygunn]

Got two purely by putting a wanted in my sig. One was with the deal on the stock and the second that another member had lying around.

Scavenging is the key.

[Brett230SX]

HUGE +1 on this one!

 

Excellent write up with fantastic photographs and superior craftsmanship!

[wash warrior]

I have a star crane stock. The reason I got it is because my battery is made for it and it was one of the cheapest solutions for a crane stock.

Since my crane stock is star, do I need to do the wire curling thing? I have a TM M4A1 still with a plastic body. I also have the original stock tube installed, not any crane stock, stock tube. Any help would be appreciated!

[Tommygunn]

Regardless of which type of stock you use the wire still has to go somewhere when you collapse the stock. If you have straight wires then they have no choice but to fold and scrunch up on each other in a random manner. This encourages kinks and wire breakage so a method like mine, which allows the wires to compress uniformally, is recommended.

[Ou811]

I hate to semi-necropost (its only a week old so I guess its not that bad)

But man that was a great idea/guide. Id totally +1 you if I could. With the amount of people who ask how to install a crane stock, this thing should be stickied.

[Tommygunn]

Nothing wrong in necroposting if it's pertinent to the topic. Since your complimenting me then that is pertinent

Anyway, cheers for the plaudits.

[Hilts]

Great job there - +1 . Glad of the necroposts otherwise I'd have missed this! I'll 'borrow' your curly wire mod if I may - I've thought about doing it but couldn't get the curls to stay permanent (if that doesn't sound too 'hairdresser' lol ).

 

What diameter/gauge is the wire you're using?

 

Thanks

 

H.

[Tommygunn]

Since it is rubbery silicone wire it is quite hard to accurately measure but is about 3-3.5mm in outside diameter and 16AWG/1.29mm inner core. Here you go:

[Lance Jackass]

A bit off topic, but will the end cover for the stock pipe go a crane stock type stock pipe still please?

 

ie if i take the stock pipe cover off a CA, will it fit on a STAR crane stock, stock pipe?

 

I hope that makes sense.

 

All riddles i tell thee

[Tommygunn]

Crumbs, that is the hardest thing I've ever read!

Theoretically yes, going by my CA, because the end cap rattles ever so slightly in the stock tube before you do the Allen bolt up tight. Therefore I would imagine there is enough margin for error to fit to other makes of tube. Not 100% mind.

Why do you ask? What is the reason for cross matching parts?

[Lance Jackass]

I'm looking at making a diemaco C8A1 SFW. Someone else on here made one by fitting a 9.6v 2000Mah battery (made up of two "sticks" of AAAs in parallel) into the actual stock tube, as the diemaco has a normal, rather than crane stock. Apparently it was done with no modifications, other than fitting a STAR crane-stock tube, with a normal stock over the top.

 

Like this:

 

 

 

 

I'm guessing the stock pipe for a crane stock is bigger than a normal one then?

[Zhang]

The crane stock tubes should be normal dimension tubes. The only differences in the crane stock tubes are:

- most have a modified cut washer to allow wires to pass through

- the buffer tube screw is shorter, as cutting down your receiver buffer is required

- on the G&P models, the crane stock tube also has its bottom section cut to allow smooth battery movement.

[Tommygunn]

The dimension are the same, give or take fractions of a mm. Note that I'm using a G&P Crane stock on my CA stock tube.

Cutting down of the receiver mounting tube, for the stock tube buffer, is NOT required and you do not need a shorter bolt to attach a Crane stock. Where are we? What thread is this?

The cut-outs on a G&P stock tube, as I have replicated, are not for smooth movement but to allow for the battery supporting yoke that holds all three sections of cells together.

 

Back to the point in hand. It is perfectly feasable that someone put 8 AAA's in the stock tube since two cells end to end would fit and leave a small amount of room for the wires. However, I would be very interested to find out the performance of this set-up as I really have my doubts about the longevity and power of AAA cells in terms of Ampage and internal resistance.

[Lance Jackass]

Apparently he uses the 2000mah one - the 16 cell version in the bottom of the picture. But i just can't see that going in a stock tube at all.

 

Anyway, cheers mate.

[Tommygunn]

8 cells, yes, 16 cells you can forget it.

Try and see if you can find the post as it would make very interesting reading. Was it on here or elsewhere?

They would really need to be high quality cells with good discharge characteristics to have any usefulness.

 

p.s. the only way he could use 16 cells would be to never collapse the stock! Still you would have a theorectical ROF voltage of 16 x 1.2 = 19.2Volts which is nuts.

[Hilts]

Thanks for the wiring info Is that the same stuff that needs the tabs filing off inside the GB shell? (I can't really tell from the original pics)

 

p.s. the only way he could use 16 cells would be to never collapse the stock! Still you would have a theorectical ROF voltage of 16 x 1.2 = 19.2Volts which is nuts.

<{POST_SNAPBACK}>

 

That 16 cell AAA pack looks like it's wired in parallell - 2x8x1000 mAh cells giving 2000 mAh @ 9.6v

 

*EDIT* The stock might collapse if you araldite the tube on and don't use a screw and washer.

[Zhang]

The dimension are the same, give or take fractions of a mm. Note that I'm using a G&P Crane stock on my CA stock tube.

Cutting down of the receiver mounting tube, for the stock tube buffer, is NOT required and you do not need a shorter bolt to attach a Crane stock. Where are we? What thread is this?

The cut-outs on a G&P stock tube, as I have replicated, are not for smooth movement but to allow for the battery supporting yoke that holds all three sections of cells together.

 

Back to the point in hand. It is perfectly feasable that someone put 8 AAA's in the stock tube since two cells end to end would fit and leave a small amount of room for the wires. However, I would be very interested to find out the performance of this set-up as I really have my doubts about the longevity and power of AAA cells in terms of Ampage and internal resistance.

<{POST_SNAPBACK}>

 

From my own experience installing a crane stock, cutting down the stock tube allows batteries to fit in the buffer tube without wires getting too scrunched up. In this case, you would need a washer with a hole in it for the wires to pass through and a shorter screw as well. I'm sure you can get away with not doing this, but most crane stocks would benefit from this and instances of twisted wires or sudden shortouts would be highly reduced.

 

I'm sorry if you misread my comment about the slit in the G&P tube. Yes, it is for the y-shaped battery holding mount, but basically what it does is the mount keeps the batteries in place to allow smooth movement and wire snagging.

 

I've attached the G&P crane stock manual - give it a read if you want to. It clearly spells out the modifications that make crane stocks easy to work with, and it points out what is likely to happen if you don't do these modifications.

m4battstock_copy3.zip

[Lance Jackass]

Tommygunn - heres the original post:

 

http://www.arniesairsoft.co.uk/forums/inde...0218&hl=diemaco

 

I would imagine that he's done away with the stock tube end cover, extended the stock, fitted the battery and then put the guarder butt pad on. So the stock could change position when there wasn't a battery fitted, but would be fixed out when there was one fitted.

 

I'm still not convinced that i could get 16 cells in there though - in my CA stock tube its a push to get 3 in the diameter of the tube, let alone 4.