@heroshark, jimbo68: Thank you!
@TeowneD:
The stock is homemade by my teammate, who is a carpenter in real life. It is made exclusively for the TM M3, so it didn't need any mod. The butt-plate is came from a cheap ACM Mossberg. Unfortunately the stock is thin in some point, particurarly where it fits to the body, so I will strenghtening it.
By the way, I think the original pistol grip is more comfortable.