I have never owned a Belgian percussion dbl, but Vernon Starr in his little book on ML shotguns stated that Belgian ones were normally brazed & English ones soft soldered. My I Hollis has held up quite well over the years. It does bear proper Birmingham Proofs. It does seem to be a rather late gun for percussion as it has the proof mark for combined provisional & definitive proof, which wasn't introduced until near the end of the percussion era.

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