***Go back to the drawing board and learn how to hold and shoot a gun properly because what you just stated in your post is not correct! A gun should be held firmly into the shoulder and not be allowed to jump all over the place like it has to be doing if you shoot the way you describe. When you are shooting slugs you are shooting the gun like you would a rifle and need proper breath control along with several other things just like trying to shoot good groups with a rifle. Your statement about a 28" barrel would probably be true since most shotgun barrels designed for small game were that length and some were even 30". It could also be the fact that the choke in that particular shotgun is too tight. Most rifled slugs are shot best through an open choke and normally will not shoot good in chokes any tighter than modified for the most part. A difference in chokes may have been the difference in one member stating that the same two guns he and a relative had shot slugs differently. What is the choke in that old gun you had problems with?

I own four 20ga slug guns all rifled barrels all using Remington Accutip 3", they each have there limits.

Savage 220f, no doubt I would take a shot at 200 yds plus
H&R Ultra Deluxe, 175 yd limit
Remington 11-87, 150 yd limit
Mossberg 500, 125 yd limit

Remember all guns may shoot well, but they have their limits

No it should shoot better than that with a 28" barrel

With a shotgun holding is so lose is probably the problem. The slug doesn't leave the barrel fast enough and the recoil effects accuracy.

You don't have to hold it with a death grip just try to guide the recoil straight back so the barrel doesn't jump.

Do you use a lead sled to sight in?

Well, the front of the gun is on a rubber V stand, the back was sitting on a pad..

Shooting style seems to work fine with my 870 slug gun... Although I'm firing hornady sst at 2000fps.

I didn't know that there was an issue with velocity and recoil as you are implying.. I always thought it didn't matter what weapon you were firing, the projectile was long gone before the kick happened.

Nope. And it don't matter what slug or how fast its going is irrelevant. The recoil begins the instant the powder begins to ignite, long before the projectile departs the barrel. And holding the weapon loosely will without question have an ill affect on the accuracy of that projectiles ability. You must maintain a snug hold upon that weapon, not gorilla grip it, just snug into the shoulder pocket by firmly pulling straight back into the shoulder by both the stock and forearm. Squeeze the shot off after aquiring correct sight picture.

It would have less effect with a shorter barrel and faster slug but yeah it definitely matters.
You can probably improve the accuracy of the 870 as well.

Give it a shot.

Should have bought the cantilevered slug barrel for the 1100.

I have the 220 as well and the thing is a tack driver. the longest I have killed at is 150yds but practice out at 200.great gun !!!

One thing I can't understand is that with today's high tech slugs, people still using 26"/28" field barrels with slugs, then drill and tap the receiver for a scope, we have three guys in our camp that do this, all three using rifled slugs none of them able to get decent groups at 50 yds, I even saw it at the range last month and last week from strangers. I do my best to explain to them the benefits of using a slug barrel (smoothbore or rifled) if your going to use a smoothbore at least get one designed for slugs, or better yet get a rifled/cantilever barrel