Ruger Ranch Rifle? Not exactly a long, high accuracy barrel length there. 4" at 100 yards sounds like a combo of factors but probably not just Lady Bugs.
Buy some new ammo and try it again...
Ruger 10/22, small .22lr carbine that with good brand new ammo gives good accuracy out to 300 feet normally.
Some of the shots seemed soft, the puny kick of the 10/22 seemed even punier on those.
They were off by as much as three inches at most.
But the rounds that still had oomph to them were dead on out to 300 feet.
(Range is a small range.)
Pretty much I figure I will have ot burn up the remaining 250 rounds and buy new ammo.
Especially since the rounds have been sitting since 1998.
(Had a heck of a time finding a range.)
Egads those ladybugs.
Looking out over the range was like looking oito a room and watching thousands of dust motes swirling in a sunbeam.
Only these were bugs outdoors.
And there were thousands of them at least.
Guy at the booth next to me went "Augh!" and looked at the end of his scope, ladybug had crawled into his field of view.