Under the situation you describe i think i would be more concerned with whether or not the slug would stop the buff than if it would blow up the gun. For steady use I think they would be unadvisable, but not likely to totally wreck the gun with two shots. I think that I would accertain what size choke the slug would go through & not use a tighter choke than that. I do believe though the Brenneke's are designed for the ribs to compress & go though a rather tight choke without damage. Many of the German guns were choked quite tight, & I do not recall seeing advise to not use them in such guns.
Miller

Miller/TN
I Didn't Say Everything I Said, Yogi Berra