Airsoft (氣槍), I believe started from US & Europe earlier some time, then in Japan around 70-80's as far as I remember. I was so impressed Japanese engineering when I was teenage. Owned a lot of Tamiya models. Then airsoft came into Asian market. It was so nice and made by plastic body with some metal internals. The body design was based on RS with trade, and functional also. That time there were no blow back function. From time to time, they improved it not only the look more like RS, but also function like RS too. Because the power was using 134 gas, this Japanese engineering designed the internal so complicated and detail to make out the functional similar with RS as well, some with shells and some don't. If you've disassembled those Japanese airsoft guns, you will know what I mean. As of the market is changing, asian market turned this design into metal base from body to internal. Now not only the look, the internal, the functional, the weight, even the power and sound. Fulfill most of our airsofters and collectors needed!
PS: I know there are original parts available in Japan for its own products but not available outside Japan most likely. Only some from Taiwan, unless you can get connection or source direct to Japan.
Shotgun Comparison Chart
*This is based on personal experience, and it is for a reference only.
APS CAM870/Custom SF
Hwashan Double Barrel
Marui M870/Breacher
Marushin Mossberg M500
Maruzen M1100 revision semi-auto
Maruzen M870
Tanaka M870
