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The AGM MP40 Barrel / Hop fix.

This is a guide based on the Taffy mod that first appeared on ASCUK, I have

added a few more pics & refined a few parts to make it more easy to understand.

Please note this involves a destructive method which could possibly leave you witha broken hope unit, this modification is done at your own risk & I will not be held

responsible for any damage or adverse affects on your gun.

The benefits for a successful modification will be a more accurate gun with greater

range & should also prove a power increase, the standard AGM barrel is a very

poor quality & way over size in internal bore & the hop unit as standard can not

be opened up as it is glued & non serviceable as standard.

The parts needed are a replacement inner barrel of 229mm in length from either a

TM mp5 or similar & a replacement clear silicone hop rubber, this is important

for easy line up on the barrel, I opted for a 6.04mm TM compatible Systemabarrel,

Parts list,

1x 229mm Systema 6.04mm barrel, aprox 17.50

1x Guarder clear silicone hop rubber, aprox 6

parts sourced from ehobby asia & price includes postage.

Tool List,

Small & medium Phillips screwdrivers

Coarse abrasive paper

De greaser

Thread lock

Superglue

12mm insulating tape

Craft Knife

Junior Hacksaw

Dremil type tool or small file

When using hand tools such as craft knifes & power tools always wear gloves &

eye protection.

Step 1.

Remove The two halves of the gun, take the upper receiver / barrel part & remove

the 4 screws that hold the barrel unit to the receiver, ( two are in the magazine

well)

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when the screws are removed pull the magazine well plastic liner out:

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then separate the barrel from the receiver, undo the two small screws that hold the

hop unit to the outer barrel unit & withdraw the hop unit & inner barrel from the

outer barrel:

now the hop unit & inner barrel have been withdrawn undo the two small screws

that hold the hop adjustment slider on & put them safe, now an extra small Philips

screw can be seen which hold the hop lever into the hop unit, this can be left in,

now take your junior hacksaw & cut around the moulding line in the hop unit, cut

right through to the barrel, see pic, cut where red line is:

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once cut it should look like this:

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you should now be able to slide the cut part down the barrel, we will call this part

barrel spacer 2, on the barrel before you cut the hop unit you will have noticed a

circular black ring, we will call this part barrel spacer 1, holding the hop unit in

one hand & the barrel in the other pull apart, it may take some strength as glue

from the factory may have it partially stuck, when the barrel comes free you will

have part of the inner hop unit on the barrel,

Remove the small plastic clip that holds the barrel, the inner hop unit should now

come off, discard the hop rubber & the hop bucking, clean any swarf out of the

hop unit, discard the barrel retaining clip, now cut the inner hop unit as shown in

picture, the part on the left we will keep & call it barrel collar discard the other

part,

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Now comes the re assembly process, take the 3 previously recovered parts barrel

spacer 1, barrel spacer 2 & barrel collar & either using a file or dremil type crafttool abraid the inner surfaces till they are big enough to fit over the new barrel,

the new barrel is larger in diameter than the standard item, it important they need

to be a good snug fit & not to loose, de grease all 3 parts, now abraid the new

barrel & de grease, its essential to have no grease on this so the glue sticks, now

look at the new barrel, you will notice a small line machined in it on the opposite

side to the hop hole, slide the part barrel collar onto the barrel, this should be a

good snug fit & not loose, line the small grove in the plastic with the grove in the

barrel, & put it into the outer hop unit, the grove in the plastic barrel collar

lines up with a grove in the hop unit, ensuring the alignment of the hop hole in the

barrel,

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now comes the hard bit, without twisting the barrel push the barrel collar into the

hop unit so its flush the hop unit,

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Keeping the hop unit & barrel collar in the position above move the barrel so it

aligns the hole in the barrel right in the centre of the hole in the hop unit, you may

need to pinch the hop unit with pliers so the barrel collar stays flush with the hop

unit as you move the barrel in & out, its important not to turn the barrel, when

the hole is lined up right put 1 drop of superglue between the barrel & the barrel

collar making sure it does not go on the hop unit,

After applying the glue & leaving it to set withdraw the barrel & barrel collar,

check the line on the outer of the barrel collar is lined up with the line cut in the

barrel, if its not pull the collar off & start again, if its ok put superglue right

around the the barrel letting it run in between the barrel & barrel collar, do this

with the barrel out of the hop unit, see pic:

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Once the glue has dried push the barrel & collar back into the hop unit so the hole

is aligned in the hop unit & the collar is flush with the front end of the hop unit:

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Now slide the part barrel spacer 2 that we cut of before down the barrel & glue

in place so its butted up against the barrel collar & hop unit, then slide the part

we called barrel spacer 1 down the barrel & glue it in position so its right up

against barrel spacer 2 when the glue is dry withdraw the barrel from the hop

unit, the barrel will now have the 3 parts attached & it should look like this:

now you notice the hop rubber is too long! Not to worry, trim about 7mm off the

end with a knife:

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now slip over the hop rubber onto the barrel & tape on with good quality 12mm

insulation tape, this needs to be good tape as there are crap brands out there, it

should look like this:

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now insert into hop unit, if you have done everything else correct it should now be

perfectly aligned,

now fit the hop bucking / spacer part:

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then re attach the hop adjustment slider, you can now see the perfect profile of the

hop rubber when you add hop, note on these hop rubbers even with the hop right

off you may see a slight protrusion of the rubber through the hole, this does not

affect the use of the gun, a smaller diameter hop bucking could be fitted to remedythis but I have found it not to be a problem, I have successfully done 5 of these

conversions so far,

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Now to stop the barrel rattling around at the front of the barrel wrap insulation

tape around it, then insert the inner barrel & hop unit into the outer barrel, it

should fit ok & the barrel spacers should butt fit right up against the outer barrel

making it a tight fit stopping the barrel moving forwards, on one I did there was avery slight bit of play, I fixed this with a little instant gasket applied like in pic:

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fitted:

job done, now fit the barrel into the upper receiver, fit the plastic magazine liner

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& the 4 screws, the shorter 2 go into the magazine well & the longer 2 go through

the outer receiver, ( on early ones all 4 screws may be the same length) I put

thread lock on these screws as I have had them come loose!

Put the 2 gun halves back together & try it out!

This example was chronographed at 311 fps, it also fired to the left, after the mod

it was consistent at 332 fps & fired straight, the range was dramatically increased

also..