personally, like the man above, I choose the old-reliable compact .38 for my ankle gun (640-2), but one guy on my shift wears a 27 in the desantis ankle rig and he says it has served him very well. It looked very well made.
Personally, I rarely wear any ankle holster without boots, as I have found that they too frequently slide down too low, if they don't have that boot to rest on. of course, that could be my little chicken legs causing that problem
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