Zing cases
Zing cases
I tried one of these from either Adorama or B&H whose description indicated that it would fit an M body & lens. The "stretch" over lens opening didn't hold on my 35 and was borderline on my 50 When it doesn't stay engaged there isn't much to hold the case closed and it would flop open while carrying it on my shoulder. It worked acceptably well with my 90mm attached, but it's still not a snug, stretched fit around the body. It is good as a wrap for in bag protection though.
All it really needs is some velcro sewn into the back of the lower "half" and the lip of the "pull-over" half to work acceptably well with the smaller lenses. Since I'm a worse seamstress than I am a photographer...I went after a used black eveready case and leave the top half home. I wrap the M in the half case and whatever lens is attached in the Zing when I tuck it away in my backpack.