I actually prefer the cantilever mount on the barrel over a receiver mount on a shotgun with interchangeable barrels....however I don't like either one.

My shotgun is tapped and receiver mounted but its not an interchangeable barrel shotgun. A tapped barrel on an HR is also a good setup.

I'm not a big fan of pumps or autos for slugs at all really. I'd go single shot or bolt action....there is a reason they are the most accurate and consistent slug guns on the market.

I have many Slug Guns, of course my Savage 220 hands down is my #1 gun, 3/4" groups at 100 yards, 1.5" groups at 200 yards. But I do have two 1187s with the rifled/cantilever barrel topped off with Leupold VX-II 3-9x40......The 12ga Accutips 2-3/4", the 20ga 3" Accutips, and both shooting great, not as tight as the Savage but very accurate

The savage is not only a great shooter but also varies much, much less from gun to gun,is much less picky about slugs, and much more forgiving to shoot.

I set the guns in the sand bags on the bench. I pull the gun back into my shoulder while pulling the forearm down onto the front sand bag. Not overly pulling it back or down but enough to keep it steady and from jumping off the front bag.


If I don't do this to the 12 ga. the front will fly up and off the bag.


NYH1.

How do you hold your 1187's on the bench when sighting them in?


NYH1.

He's having problems with accuracy, in a sub par slug gun set up. He's tried numerous remedies.

It answers his issue succinctly. Savage 220's are known for accuracy out of the box.

make sure the barrel is flush to the receiver, and there isn't any wiggle in it. Friend just got the 1187 20ga slug gun, and it got sent back to Remington, the receiver seems to have been milled to wide giving the barrel wiggle room......also check your scope mounts are secured

I use this rest, made by Caldwell it's called the Matrix, about $40/$45 from Dicks Sporting Goods......

I hold my shotgun firm to my shoulder, left hand lightly on the barrel

So HOW do you know those guns are capable of 2-3" groups?

I had trouble with Lightfield slugs in one of my guns. One time I'd get a GREAT 3 shot group. Make the appropriate adjustment. Then the next shot was a mile off. I'd shoot THREE for a group and it would all barely fit on a 5 gallon bucket.

I'd go through all kinds of wasted effort and it would shoot an awesome 3 shot group. I'd make an adjustment and dejavue all over again.

Finally came out one day and just sat down and shot FIVE with no changes and three looked awesome, the other two were like a gorilla fired them. Up until then I was convinced Lightfields were the most awesome slugs on the market.

I always let the entire gun return to ambient temperature if it starts to warm up even 5 degrees.

I use a laser therm gun to keep track of barrel temps.

When I'm hunting the FIRST shot is the only one that really counts. They won't stand still for practice and warm up shots.

My 12 gauge 870 with a Hastings cantilever barrel loves Remington Buck hammers. My shoulder hated them while on the bench. Deer hated them while in the field. Remington no longer makes Buck Hammers.

I thought the cantilever setup was awesome as I could remove barrel and scope as a single unit from the receiver. Last years bench session with my 870 made me switch to a muzzle loader. I will never look back.

Several friends have the Savage 220 and love it. However, there are issues working the action. Have another with a 11-87 and it drives tacks. To the OP, the best advice already provided is to have someone else shoot your gun or get different one. Although you seem adapt at shooting, it sure seems you have checked every possible variable except yourself.