sorry! it was a rushed explanation.Thank you for your answer. I'm sorry I didn't really understand what you explained to me about how to do with magnets. Could you rephrase please? Thank youuuu
Gluing two pieces of plastic together is just to make it easier for magnets to be inserted in. If you cut a hole in the plastic and glue a circular magnet in it will be hard to stick it in as you can only glue the sides. The magnet will also be visible from both sides and possibly fall out of the hole over time. The second piece of plastic acts as a barrier/backing for the magnetic to remain stable and also helps things look neat. With plastic behind the magnet, it can be glued in more securely and not fall out as easily.
Then you can just simply glue a magnet to the gun or if you have a plastic gun you can pry it apart and fill it with small magnets.
I did a quick drawing if that would help with the explanation, I also got the idea from a YouTuber called Odin makes when he used magnets to make his Loki horns detachable. (I've linked the video if you want to watch it Here, time stamp 7:58) He used a thin poster board as a 3rd top layer but this is not necessary. He also does a tutorial on a winter soldier mask and goggles Here if you want to check that out as well.
Also with Usagi Pilgrims' idea for using a gun mount, I think it could work really well, the gun mount comes with a strong tape that you could glue to the plastic if you don't want to drill into it. And with my method, you are already gluing magnets to your gun this will work as well. The only problem is that I live in Australia and 2 of these would cost me around $70 with shipping so that idea is out of the bagThis might be an option. I use these for concealed carry on a vehicle, & stashing my pistol in different places. They're $15 a pair, can mount with screws but also come with 3M mounting tape, they're coated with rubber on the outside so as to not scratch your weapon, & are rated to hold 45lbs.
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Believe me when I say THEY HOLD! I use them regularly to hold a Glock 27, but I've also had one hold a sawed off 12Gague under a cabinet.
I don't see why they wouldn't work for a costume.
Let me know if you need any more clarification.