Hello JayCee.
I am no expert on pressures, so I don't know the effect it will have on your gun. If the chamber length is correct and the gun is properly proofed I wouldn't worry too much.
What I have found is that some of the foster slugs, such as the Remington, tend to be relatively small in diameter. Within the past few years, Remington changed the diameter of the 12ga slug that they were using. They made it a bit larger than it used to be so that may change things a bit. Those fosters are made to pass through most chokes just by design as Carl mentioned, but I really can't say how it would act in your gun.
In the past I would have a few different slugs cut out of the shells and the one that fit the bore the closest usually shot the best. It would definately let you know just how close a fit it is.
Buenos Suerte.
Tom
