Didn't fit well - Pro Mag Winchester Models 52, 57 / 69 .22 LR Rifle Magazine

This may not apply to all the promags made for the Winchester but in my case it wouldn't slide up into the magwell far enough for the bolt to engage the round. I could see where the upper part of one side was catching. I was able to remove enough of it with a dremel tool to make it work. I compared with a factory mag and measured it. It was only a couple hundreths too wide.