I know this topic has been beaten to death so please forgive this newby for asking again.
I did do a search on this topic and found a compelling argument from Jim from Arizona as to why firing a rifled slug through a full choke is perfectly safe. viewtopic.php?f=2&t=8852&start=0
I have no reason to question his wisdom on this matter, nor anyone else's. While I have owned shotguns for most of my life, I never really looked into them - particularly where slugs are concerned -- in much detail until very recently so I am on a steep learning curve. Hear me out.
I hauled apart, 3 different types of 12 ga rifled slugs and took some measurments with a set of precision calipers. Here is what I found:
1. Winchester Rack Master High Velocity Slug 3": This slug measured 0.731 inches in diameter. The hard plastic wad behind it, measured 7/16" thick (with a 1/4" cone that projects into the hollow of the slug) by 0.736 inches (diameter).
2. Remingston Slugger Rifled Slugs 2 3/4": This slug measured 0.730" in diameter. The hard plastic wad behind it measured 1/4" x 0.740 inches (diameter).
3. Winchester Super X Magnum Rifled Slugs 3": This slug measured 0.714 inches in diameter and is backed by 3 cardboard wads each measuring 0.738 inches in diameter.
OK. Where am I going with this you ask?
Simple. The bore of a 12 gauge is (in theory anyway) 0.729 inches. A full choke would be 0.729 - 0.035 = 0.684 inches.
Now I accept the collective wisdom on this site that foster slugs (sorry, all three examples were Foster slugs) will compress and deform as they leave the muzzle. But I wonder just how much those hard plastic wads that back the Remington Slugger and Winchester(Rack Master)deform or if they deform at all. Certainly they are a lot harder than lead and I reckon less likely to deform/compress.
If I were to play it strictly safe, it seems to me that the Winchester Super Xs would be a safter bet with a full or modified choke.
Oh ya, one more point: none of the boxes containing the ammunition provide advice on what choke should be used with the product; nor are there any warnings not to use them with a full choke. Jim mentioned the issue of liability which is a good point and which suggests that the ammunition can be used on a full choke.
But there is that pesky math to contend with.
Gents, I am not trying to pass myself off as an authority by throwing this out. I would very much appreciate any comments on this topic. I read recently that at one time, rifled slug diameters were significantly smaller than the bore of the shotgun but that recently, they have been made larger to create a better seal as it goes down the barrel.
If I am out to lunch, feel free to tell me. I don't mind being set straight.