I made one a couple of years ago that was a little different. I made the strap three square knots wide to spread the load on the neck, rather than use the standard single square knot over filler. That's a nice design you've got, but I'd still be a little concerned about the comfort around the neck with a full load.
I feel slightly sorry for a man who has never patterned his gun, who has no idea how far his chosen load will retain killing penetration. But I'm extremely sorry for the ducks he shoots at beyond the killing range of his gun and load - Bob Brister