boren wrote:To all those who are in favor of flat tampers, are you using flat baskets (doubles)? If so, it makes sense that such tampers would be optimal, as they apply equal pressure throughout the basket. With single baskets (usually with slanted sides) flat tampers would probably not be as optimal, and curved tampers may more closely match the profile of the basket.

I have a 49.4mm flat, 49.05mm flat, 49.0mm convex and a 48.7mm flat with a rounded edge to match the step in the Elektra single basket. The 48.7 is the most reliable. I had high hopes for the 49mm convex as it was purchased later, but the frequency of shots with side channels was the same as the 49.05mm flat. (The 49.4mm was just too wide.) Someday I'll turn down the edge of the convex just because I like the feel of that tamper's handle, but that's a low priority.

On the 58mm side, I have a 58mm Reg Barber C-Flat base that made no difference for me in comparison to a flat, even with the old-school slant-sided baskets that come with spring lever machines. The only thing was nutation seemed easier/better with the C-Flat, but nobody does nutation anymore ...