The good news is that I found 'it'. The bad news is that there's 2 of 'em, they're very different, and you have a choice to make. Options are good!
First, I'll attach 3 photos I hastily snapped yesterday. They're crummy photos mainly because for various reasons I didn't want to swap lenses on my camera to something more appropriate for the task, which resulted in among other things, zero DOF (depth of field); however, they're good enough to illustrate the difference between the 2 reflectors and how that affects reflected light.
I couldn't do an A-B comparison in my 3-cell MM because I have only 1 alkaline AA in the joint, didn't want to use L91s and risk OV damaging one of my few examples of that rather unusual bulb, and Eneloops won't fit in my MM because it's old and the tube bore is too small for those. What the photos do illustrate is the difference in the effect they have on 'incident' light from my flash reflecting from their surfaces, and this is very similar to the effect they would have on reflected light from an installed bulb.
Here's my verbal description to go with the photos:
First, forget my "brushed" description of the finish(es), because that was a poor choice of words.
They both appear to be machined to the same specs, and are (to my eye w/o my calipers which aren't handy), dimensionally identical. They both have very slight machining marks, but the scale of those makes them a non-factor optically. They are both 'smooth', meaning there is no level of 'orange peel', 'egg shell', etc., and the only real difference is the fine surface 'finish' itself. I would describe the one on the right as a 'mirror finish', and the one on the left as a lightly 'frosted finish' (rather like Scotch Magic tape).
Although I can't compare them today in my MM, from what I recall the effect of the 'frosted' finish was a more homogenous, even, consistent beam with significant reduction in the reflected effects of artifacts / defects in the light from the bulb itself on the reflected beam being projected, resulting in enhanced resolution of detail in the surface of the object being illuminated. This may well come at the cost of a few candelas on that object downrange, but downrange ain't very far with a MM, and I believe any loss was more than offset by the reduction in optical noise / defects / artifacts / distortion, which personally I feel is the 'enemy' when examining objects / surfaces at shorter distances. I think that's why the 'frosted' one ended up in the 'user' I have left (which wasn't ravaged by alkalines).
That's 'seat of pants' opinion, but the bulb setup you're using is far different from the one in my light, and I'm not the one making the decision either. Perhaps you, and certainly others who have more experience with experimenting with incan lights / mods will have a far more informed opinion that mine based on my very limited experience, so I defer to the experience of others to decide / advise on what would be best for your application. I will only add that the 'frosted' reflector is what TacStar shipped standard with their MM upgrade kit (although they also supplied the 'mirror finish' one to me on request), so I guess that indicates what their opinion was for that setup - but again, that uses an only slightly larger version of the standard MM bulb w/ higher voltage rating, and I gather you're using a bulb rather different from that. @bykfixer and others will have more experience and more valid opinions than mine.
Let me know which one you'd prefer to use, and it's yours!
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