Making PPS 870 cartridges

I would like to thank ljerr2 for showing that a PPS 870 can be converted to a cap gun. At first he modified the 870 and a CAW Mad Max cartridge. Then he made a custom cartridge from dimensions of the CAW internals and the 870 externals. That allowed it to be used with no modifications to the 870.
https://mp40modelguns.forumotion.net/t4899-airsoft-to-modelgun-870-pump-shotgun

After seeing his work I ordered a PPS to use in building a Aliens Pulse Rifle. I was also able to get a set of 2 of the CAW cartridges from him. After having the parts for a few years, I finally started working on the Pulse Rifle.

I found a print of the m40 grenade and modeled it in Fusion 360. The od was slightly too big to fit the PPS so I adjusted the dimensions. I measured and modeled the CAW internals, but they were going to be too big to fit. They would work for a regular shaped shotgun shell, but the m40 has a groove that is too deep. I decided to shrink the od of the internals.

I 3d printed a cartridge, but I screwed up a couple of the dimensions so it didn't work. I made the changes and a few minor ones and started printing again. Hopefully I'll be able to test fire it in a few days.

nice work

Ran into a bit of a problem. The m40 cartridge can't be fully inserted. In the chamber there is a ring that the PPS cartridge slides into.

For now I'm going to redesign the cartridge to match the PPS cartridge. Once I get a working test fire I'll try the m40 again.

Everything for the new cartridge printed perfect except the anvil. The tip is small and deformed while printing. I'm going to switch to using a roll pin for the tip.

It fits the chamber and cycles just like the PPS cartridge. The extractor does damage the rim. The base is going to be a consumable, but should be good for a few firings. I'll probably modify the base so the PPS metal cover can be used.

I was unsure if the anvil would work so I loaded it up with a kids toy cap. It took a couple of tries, but it went off. I loaded it up again and it worked.

Next I loaded up the model gun cap and it also worked. It's several times louder than the kids toy cap. Once I remake the anvil I'll give it a try with it loaded with 7 caps.

It's always cool to see creativity and ingenuity at work to make things that aren't otherwise available!

I am still surprised there is not a commercially available pump 870 modelgun besides the old MGC version. The PPS feels pretty darn good due to it's metal construction.

Interestingly enough, I think I've found that if you make a cartridge for the PPS870, it will also work in the Tanaka 1897 shotguns! Huge bonus option. (Will require removing original equipment detonator from Tanaka first).

By the way, due to unforeseen personal circumstances, I will likely be selling off one of my PPS shotguns. It would be a brand new one!

Nice work! I was working on the same thing a while back. Looks like we ended up in pretty much the same place. Been meaning to revisit it to get everything working 100%.

Veektohr that looks pretty good. Did you shorten the cartridge to fit or did you modify the chamber?

I did a test fire with 7 caps.



I had a decibel meter set up at the rear of the stock. It read 72 decibels at the max, but I don't think it is right. It felt a lot louder than that.

The cartridge broke during the test fire. The base split at the start of the threads. This might be from a printing issue. The rest of the parts still look good.

I changed the anvil to use a roll pin. It's super glued in so I wasn't sure if it would hold up to firing. It looks like it's sill ok.

I still need to bore the nose so that it will chamber properly. Here is a test fire with a brass prototype (Mad Max shell copy basically). 7 caps w/ prop powder & some styrofoam wadding.



PS if you have any questions about the pulse rifle build hit me up. I spent years working on this one. Sadly it wasn't even for me so it's gone now lol. But it has a very happy home. Anyway, I learned a loooot of hard lessons about how to fit everything together. I guess I should post some pictures of it here.

Veektohr yours look like a bigger flash. Looking at it in slow motion it was a pretty big fire ball.

When I looked over my video again I saw that just after the flash there was still some burning going on. I didn't have the airsoft internal barrel installed. Maybe that would have helped.

Punisher wrote:

Veektohr yours look like a bigger flash. Looking at it in slow motion it was a pretty big fire ball.

When I looked over my video again I saw that just after the flash there was still some burning going on. I didn't have the airsoft internal barrel installed. Maybe that would have helped.

I think the prop powder & wadding is helping a lot with that big flash. When you say airsoft internal barrel do you mean the plastic cone thing that pokes about three inches into the aluminum barrel? If so, I left that intact since it helps hold everything together (keys in with the lower mag tube block), which would definitely direct more of the flash down-barrel as well.

I was talking about the 6mm barrel. It might help keep the flash better contained until it gets to the muzzle.

Looking over my video again there is the main flash. Then a few frames later there is a secondary flash. When I disassembled the cartridge a few of the caps were pressed together so maybe the 2nd flash was from a cap going off late.

Could you give some details about the prop powered and wadding?