Wow thats a sweet replica, are you putting a real Taurus Model 85 in it
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For the holster your best option is leather, or follow the trend most police are and use plastic (fehhhh!).
If leather, your going to need to test a few grades, not so thin it does not retain the shape and not to thick it's to annoying to stitch.
Draw an outline in pencil where the straps go off if a shoulder holster or where the loops will be if a belt will be on your backing leather. Cut or attach loops with rivets at this time if its a belt holster.
First put down you backing leather (dry) then place your pistol on it. Using wet leather on the top stretch it just slightly tightly over the gun and see if you can get it to shape over it.
Don't cut it until it's done slowly punch and stitch it around the gun keeping in mind you need it loose enough to enter/exit
After it's all stitched cut the backing close but far enough away not to weaken the leather from the stitches. Now cut the top layer to bend/fold over your edging and stitch that through the same holes to give a nice finished edge.
Leave the gun inside the holster until it drys and put some folded up paper behind the gun to fight shrinkage and make the gun details show through the leather.
For Plastic
If your going modern, get some black plastic,kydex or whatnot and heat it up enough with a heat gun to be pressed over your gun but not enough so to stick to it. Drill and "rivet" using bolts and nuts or Chicago screws to attach front to back.
These are just really basic advise as I'm not sure what kind of rig your looking for.
Have you also considered tactical cloth style holsters?