Patterning on Target

I admit, I am a newbie when it comes to owning and firing a shot gun. I recently aquired my grandfathers Remington Sportsman 58, 16 ga shotgun and after a good cleaning, took it to the local shooting range.

I fired a box of old shells and noticed that in addition to the spray pattern of little holes that I expected I found several large holes as if a 16 ga bullet had passed through the target.

Can anyone please explain this to me.
Thank you.

hi dq,
if your close to the target, older shotshells used paper wadding to hold the shot in the shell, newer shells use a plastic plug. i would guess that the wadding or plug is going to and thru the target.
Kim

I thought it might be something like that.
Thanks.