If your going to use it in the model 19 frame with a 32 barrel you can leave the recesses as the model 19 frame lug is set for a counter sunk cylinder. But, if you use it in the 16-4 frame you will need to shave the countersunk portion of cylinder off or trim back the 16-4s frame lug. Something I would not do as a stock 16-4 commands a premium price.

If you trim it back and use it in both frames for some reason, it would still work in the 19 frame. It is just that when open the cylinder would move back the .04 to hit the frame lug when ejecting and as you load the cylinder it will move back forward and close normally. If you were to hold itt muzzle up the side of the ratchett might hang up a bit on side of recoil shield, but then your ammo would be falling out anyway if you did that.

This is a common deal with dual cylinder 45 acp- 45 colts. The acp cylinder has a lot of space between recoil shield and rear of cylinder (moon clips + case heads) and a 45 colt just has the rim. So normally for the colt cylinder needs the lug way bag and this means the acp cylinder is real sloppy when open. There is another way on them and gthat is to cut a .04 ledge from the rear OD of the colt cylinder. This lets the lug remain at acp length and gives the colt cylinder clearance on the lug.

I did away with all my dual cylinder 45s though. The ones that I want to fire both use 45colt cylinders with clip recesses for acps.