I've did the test on live turkeys back when I shot Nitros 4x5x7's Hevi Shot....I made a bad 40 to 45 yard walking shot on a gobbler...he went down then got to his feet and flew off.
Called him in and killed him the next morning...shot him about 15 yards with another load of 4x5x7 pixie dust....like to have tore his head off.
When I cleaned him I noticed his legs felt funny....I skinned them back and there were literally 100's of small shot between the meat and skin. (I look back now and wish I had taken pictures).
Enough proof for me.....had I been shooting #4 shot or even #5 shot there's no doubt it would have broken his legs immobilizing him.
I ain't talking about no stinking heavy shot, I'm talking about the heavyweight shot. It blows the hevishot out of the water. I'm not kidding myself, I'm a hand loader and I know a thing or two about the heavier than lead shot. I know for a fact that lead #4 will NOT go through 1/2" plywood at 1300 fps. I know for a fact that federal heavyweight #7 WILL.
That's awful funny, I shot a bird low last year at 41 yards with a load of tss #8, majority of the shot was a little below his waddles but those #8 broke both legs, and both wings with pellets that entered one side of his breast and completely passed through and exited the other side.
Sounds like you shot your bird in the legs??