I had a guy bring his 20 ga 870 Express deer gun to me today making the above claim. "When I first got this gun it would perd-n-neer touch holes. Now it won't shoot for shucks with anything I try!"
My first thought was the scope. After all it was a 10 year old Simmons 8 Point in 1.5-5 variable. Probably cost $30 at Wally World when new. So he left me the gun and about 10 boxes of 5 different kinds of ammo. I replaced the Simmons with tried and trusted Nikon 4X with ample eye relief for what we were doing.
He was right! I fired two rounds of Hornady 250 grain Sabot Slugs and the first one went 8 inches high at 50 yards and the second about that much low. The results were about the same regardless of the ammo.
The scope mount is the a B-Square saddle mount that is held in place by screws through the 2 pin holes in the receiver. This is a mount that I always considered as good as any and can't remember ever hearing of one failing. The crown, if a slug gun has a crown looked ok. I put the gun in my vise and stuck a bore sighter in the hole what spits out the bullets. I wiggled and tapped and wiggled some more but couldn't get the cross hairs to move from their original spot. I then took the barrel off and held it to the light and looked through the hole not really expecting to find anything........well I'll be??? That $350 rifled Hastings Paradox barrel was full of lead from one end to the other. I can't say that I have ever seen anything quite like it. Obviously someone has been shooting the old rifled smooth bore slugs and lots of them in this barrel.
A quart of printers solution, a bottle of shooters choice and three brushes later and I could see rifling.
I didn't have much day light left when I got back to the range but had enough to fire 3 rounds of Remington Premier AccuTip 260 grain Bonded Sabot Slugs into 1 ragged hole at the same 50 yards.
I wonder if his offer to sell me the piece of junk for $200 dollars still stands?
If you have a rifled barrel on your slug gun then don't shoot the same cheap Wally World $3 for 5 pack Winchester Super X's that grandpa used in his pheasant gun. Lay down some cash for the right ammo! Sheesh!