[siggypoo]

Looks like a take on the old Motorola radio clips. Novel idea, and it's great to see you undertook to edit one yourself. I love doing that tort of thing.
I've four concerns:
I imagine that peg sticking out would be a real snag-magnet.
It might also prove fragile enough to bend or snap if impacted enough.
And, with a bit of rough & tumble, lacking a lock to hold it in place, your gun might be wooed by gravity, and joyfully leap to the unkind embrace of our dear Mother Earth.
It certainly would snag on my setup, but if the peg could be shorter, contoured to reduce snags, and a lock in place to keep it from popping out, I could see that having a very comfy home on the front of my vest.
Lastly, with slings, when you want your sidearm or whichever else, you just let go of your rifle. I can't imagine quickly and precisely remounting that to my vest in the midst of a game. But I'm not so well coordinated, lol.
Anyway, I like it a lot! I hope it serves you well.