Another battery holder should you get bored with what you already have.
I'd be tempted to make fun of someone who puts a rail on their shotgun, but I guess putting a G36 on my PSG-1 doesn't make me any better.
A working M2019 snub pistol
I love the name... "Peasemaker" ha ha ha!
and
Just incase you want to take apart your Tokyo Marui H&K USP AEP