Do NOT use a dremmil yet...
Go ask at the Beretta Forum. I hate to guide ya somewhere else, but there will be someone there who can help...
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So my Beretta 84 has the usual take-down issue of jamming when the take-down lever is rotated, and the slide/barrel/recoil guide&spring won't slide forward and off the frame. It does come apart nicely if you jack it back to the slide hold-back and let it fly forward and off into a pillow or couch. But basically, the recoil guide rod won't stay in the small under-barrel notch where it is supposed to ride. My Browning BDA does NOT have this issue, and yet the two are so similar to be identical twins.
So what's the fix? Can you Dremel out the under-barrel notch a little larger to hold the recoil guide rod more securely? Will that keep the recoil guide rod secured after a few (many) cycles of the action?
If you do a search in the Beretta Forum you can actually download
the whole owners manual for the 84BB. Or post your question.
There are some really knowledgable members on that forum.
If you ever want to turn that 84F into a two tone you can buy a
nickel barrel assembly from CDNN for under $100