The police said the unspent round did not match Kyle's weapon. It does match the ammo in the Glock.
If you have video evidence of another Glock (EDIT: or any other gun using the same ammo) being racked at the scene, please show it. There were claims previously that it came from Kyle's rifle, but it was not a match and this is attested to by the prosecution's own police witness.
I was not able to locate any other claims for where the unspent round came from after several searches. This makes me wonder if you can actually produce the claimed video evidence of another source of the same ammo.