Seems like I've taken apart four score different bolts of all types/sizes with no hassles, but this one is getting the best of me so far. A search of the net and through all of these various books has revealed nothing useful - no diagrams or instructions for dismantling the rear section - which houses the spring that drives the FP. If you can describe how or can point to a resource or diagram, such info will be much appreciated.. Straight up Model 46 with no letter as suffix.

I have a 46C. The back piece of the bolt is threaded on, standard RH thread. I had to soak mine in Kroil for an afternoon to get it loose. Some heat might help. Hold the bolt assembly in a padded vise, unscrew the front half. It is under spring pressure so getting it started again without cross threading can be tricky. Here is the thread I had on RimfireCentral. http://www.rimfirecentral.com/forums/showthread.php?t=871058&highlight=

gzig5, thanks for your explanation and for the cite to RimfireCentral as well. I have taken apart more than one 46+letter and you are right - it sometimes takes a good bit penetrating fluid and maybe gentle heat.

BUT - the bolt design of the older 46 (no letter suffix) is different in that the section to the rear of the bolt handle is a one piece tube - no seam or break - and it seems as though the knob on the very back end must unscrew in some way. In this case, it looks like maybe someone peened the tip to keep it from unscrewing. I would go to work on that aspect if I knew for certain about that design.

Any such insight on this model bolt will be appreciated.

I'm out of ammo then. I think your best bet is to post the question on the Mossberg forum at RFC if nobody here pops up. That's pretty much where the expurts reside.