Airsoft to modelgun 870 Pump shotgun

Some have wanted a little more info regarding the 870 pump shotgun videos I posted somewhat recently, so here's a quick idea as to how it works!

I started with a PPS airsoft shotgun.  This is a cheap replica of the Tanaka 870 gas airsoft shotgun.  It is a great platform to start with because it already uses a firing concept that lends itself to conversion as a modelgun.  Here's why:  The gas is contained in the shells, so the firing mechanism just needs to strike the "primer" on the shell body, similar to how a modelgun would need to function.  Now, all you really need is a self-contained modelgun shotgun shell to fit this shotgun.  

Most of us are familiar with the MGC shotgun rounds and the Hudson shotgun rounds.  Those require an external detonator, so are not good options.  CAW recently released a multi-cap shotgun round designed for use in the CAW revival of the MadMax, and of course the original Hudson Madmax.  This round is "self-contained" in that the detonator is internal to the cartridge.  You just have to strike the primer to make it "fire".  This round holds up to 7 or 8 caps and is full brass construction (if I remember correctly).    

This full brass round is extremely heavy and the rim is quite thick!  Luckily, a custom round was released in Japan that is mostly aluminum in construction, so it is quite light!  It is designed under the same concept as the CAW round, but it is more realistic in appearance and comes with two sets of shell bases, one with a thick rim and one with a thin rim.

So now, the modification is to make this round fit the airsoft gun!


The custom modelgun shell is slightly larger in width than the airsoft version, so some mods are needed to the shell and the gun itself.  For the shell, it is necessary to use the thin rim base and cut down the rim diameter.  Some slight mods are needed to the bolt face to make it accomodate the size of the new shell, as well as a slight enlargement of the extractor claw grip.  I also slightly enlarged the magazine tube bushing.  The chamber for this gun has to be removed, then slightly enlarged and carefully drilled to reduce the length of the shell guide insert so the cartridge will fully chamber.


That's basically it.  I did end up messing around with it more and doing some other fiddling and designs, but this is how the project got off the ground.  Seems like it would be easy for a big name producer to offer this shotgun as a modelgun, and I think it would be welcomed!  With the correct size shells made from the factory, this could be a modelgun with zero modifications.  Just add modelgun shells and there you would have it!

This model is quite cheaply made, but PPS offers upgrade parts which are nice and can increase durability.  For example, the plastic bolt can be replaced with an aluminum one.  Many other spares are also available.  Nice!  

The gun can be had for less than $200US.  The shells are quite pricey though at around $60US per pair, I think............

Nice! Do you have pictures of the modifications to the magazine tube / receiver? Cool to see how easy this conversion is. Makes me feel like a dumbass for shelling out for conversion a while back seeing how easy it actually was. Definitely something I could have managed : /

Sometimes seeing simplicity is complex

But you obviously spotted it and with good thing king reached a really good result. - thanks for sharing it's really inspiring

Where did you find the aluminum cartridges?

Picked up a pps 870 to use for an aliens pulse rifle conversion. Want to machine the cartridge to match the grenade profile.

I got them from Japan.
I may have an extra set I'm willing to sell if you want to shoot me a PM.

Curious to hear how all this turned out? Any video?
I have both PPS and APS shotguns for prop use, but hand't tried modifying for caps at all... I did consider loading some powder in the shells though, especially the APS shells that have a wadding.