Not too sure, but IIRC the two knives are part of BM's Mel Pardue 85x series which have the same basic design and blade shape:
- BM850 rainbow anodized Ti bolsters and ivory micarta handle
- BM855 Coloured aluminium handle
- BM856 G10 handle
Cant speak for the BM855, but i've both the 850 and 856. Generally, both are good knives, well-made and a perfect size for daily carry. Lockup is ok if you don't mind the liner having some play. They are also unoffensive enough that your co-workers won't call the cops when you whip it out to cut something.
The only minuses are the poor edge geometry on both knives and the BM856's poor access to the thumb stud which makes it difficult to open (really needs a scalloped grove on the scale next to the thumb stud). I fixed the edges with my Sharpmaker and am thinking about filing a groove on my BM856 but haven't summoned the courage yet.
Red
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"Praise not the day until evening has come;a sword until it is tried; ice until it has been crossed; beer until it has been drunk" - Viking proverb