Really, truly, awful accuracy....

[Montana Slim]

Funny you say that... a friend and I were joking that at 50 yds, I could probably stick as many in a 1'x1' cardboard box with my super D as I could with that rifle....
My longbows definitely have more blood on them than that rifle!

 

[Where's Bruce?]

Had a seating issue with one rifle. Sanded the stock of my Mauser 45-70 Govt, problem solved.

 

[Marble]

If you have access to a bore scope, or there is a smith near you, they will generally look down the barrel and will point out damage, copper or powder fouling etc.

Before I did anything major,I would recheck everything, including the ammo.

Even a burred crown will generally not be that bad.

I had a batch of AR 15s from the Army that I was so excited about. 100 yards groups were about 12"+ and the bullets were key holing, tumbling through the air. Barrels were all toast.

Something is loose, worn, broken or missing. One thing at a time and find out what it is.