Not to belabor but I've been building rifles including Savages since the early 60's and I've stuck a few bolts in most brands AND Savages. With the Savage nut, pulling a barrel is so easy and that amount of strain relief might be enough to let the bolt come loose.
I'm guessing you have some major brass/plastic extrusion going on at the chamber/boltface junction maybe back into the firing pin hole, maybe into the ejector button hole and even into the extractor slot, all of which will cause a ruckus. If that's the case...worse case scenario...you will have to pull the barrel.
WD40 is for rust removal more than anything else but it might work if it just needs some lubing up...you might also dribble in some Kroil if you have it.
DON'T hammer or use a pipe wrench or snipe on the bolt handle...they are stout but also sometimes a bit brittle and can break. Now might be the time to swap in one of those fancy bolt handles.
Most shotgun shell casings are rated not much more than 16KPSI tops as most loads, even the magnum hotties run below 14KPSI.
I can get away with a little more pressure, relatively speaking and not overpressure, in my Mossy's and Rems than I can get away with in my NEF's. Many loads that I developed in those shotguns which ejected without problems would lock up the NEF'S using plastic cases of several brands...That ejector is not supported so the brass just bulges out there, pushing down the ejector and locking everything up. It is an EXCELLENT "high pressure and stop it now" indicator...even on my rifle/pistol NEF's.
The Rem "NITRO" once fired cases worked better than the BRI Multihull in the 12 ga also and Win AA's were like the Energizer Bunny...they just kept going and going and going...as long as I kept the pressure below 16KPSI even the primer pockets stayed relatively tight, but it only took ONE "high" pressure load to ruin a plastic case.