I've had good luck over the years using Hunter's model 1100 holster. Their size #50 is made to fit your 7 1/2" Ruger. It's a simple proven design, very rugged and efficient. They are American made, have a retention strap, and are offered in left hand versions. Plus they are not expensive. Here's their website (
http://www.huntercompany.com/index.html ). I just bought a used one off eBay yesterday for $15 shipped. At my local gunshop they sell for $40 new, which is not alot for a heavy duty working holster.