Monday, June 20, 2011

Doomsayer "M4 Shoulder Stock" Mod!

The following write-up will look at changing the ERTL Rapid Fire Shotgun (RFSG) original kid-sized brown shoulder stock to a more practical M4 shoulder stock.

For those who are keen to know more about Doomsayers (modded RFSG), you can read the original mod guide by Forsaken_angel24 at the NerfHaven forum:

Note that there are many methods to do shoulder stock mods on blasters, this isn't the only (or best) way, its just something i tested and worked.

Step 1:

Get your choice of replacement shoulder stock. In my case, i got a plastic replica adjustable M4 shoulder stock.

Step 2:

Use a dremel or handsaw to cut away the back portion of the RFSG, in my example i cut it at the section with the largest opening.

Ignore the 2 black pieces of plastic in the photo, its just some spare bits from part of the cut out section that i figured could be useful to cover gaps. Didn't get to use them eventually.

Step 3:

Measure and nest a length of 13mm SingaPlastics PVC pipe inside a shorter length of 16mm PVC pipe, this will become the connection point.

Open up the replacement shoulder stock and position a 13mm PVC end-cap inside, you'll have to trim and sand down the shoulder stock internals until it fits.

Step 4:

Bolt on the connection point pipes to the RFSG shell, i used 2 countersunk machine screws to secure it to the shell. Note that the shell is in 2 layers, so i bolted it to the inner layer.

Step 5:

Drill and sand out the replacement shoulder stock until it has a rounded opening to accept the connection point pipes, then glue the 13mm PVC end-cap permanently inside the replacement shoulder stock. I also added a ring of foam padding to help cover the gaps between the shoulder stock and casing.

Photo: (Left) Original replacement shoulder stock / (Right) Modded replacement shoulder stock.

Step 6:

Assemble everything back together and connect the new shoulder stock, its complete!

The plastic replica M4 shoulder stock i used is adjustable so it could be extended to different positions. Much more comfortable and steadier when shoulder aiming.

One of the main reasons why i did this mod was also because the Doomsayer was originally too long and it could not fit into any of my carrying cases or bags! I was getting sick of carrying it around in plastic bags with all the barrels sticking out! :)

With the shoulder stock being removable, it can now fit nicely into a large padded case.

Nice! :)


  1. Where did you find the M4 replica stock? It looks really cool and would love to add it to my collection of swappable Nerf stocks. With this method of connection or by splicing in a Nerf stock connector to the stock seems to be an easy mod. Please tell me where you found that stock!!

    1. Anonymous,

      I bought the M4 replica shoulder stocks from Black-Tactical at Funan IT Mall in Singapore.

    2. Awesome, thanks! I will have to look up their website and see what they have that I want/need and can afford this check. (lol)