If you remove a barrel then screw it back on to the same torque it'll screw back on just a little farther, which will put the front sight off slightly.
If you screw it on until the sight lines up properly, it won't be torqued quite as tightly.
Often you can get away with it, but many times the barrel will vibrate loose because it's not torqued as tightly.
This is one of those things that varies from gun to gun.
Some info on barrel work:
First, the old gag of locking the barrel in some wood blocks in a vise and sticking a hammer handle or 2X2 through the frame window and twisting the frame off is a fast way to destroy the gun.
Very often either the frame will bend, or the frame will crack.
Look at the frame under the barrel where the yoke seats. Note how thin the metal is in that area.
Using a handle or stick through the frame puts tremendous stress on that thin area, and it cracks right through the threaded area.
Once cracked, or the frame bends, that's it, the frame is ruined.
To do barrel work you need a revolver frame wrench with polymer inserts that fit that specific brand and size frame. This wrench supports and spread the stress and prevents damaging the frame.
Brownell's carry several brands:
frame wrench at Brownells
Second, very often when you screw a different barrel on, shocker..... the front sight is off, often WAY off.
Barrels require extensive fitting using either a lathe or a barrel shoulder bench trimming tool.
In order to get the barrel to line up with the front sight at 12:00 O'clock top-dead-center requires cutting the shoulder, and that needs the lathe or bench tool.
The barrel has to screw on and stop a certain distance short so that you can torque it in place so the barrel doesn't vibrate loose, which is where we started.
Next, a different barrel will usually need the rear trimmed to set the proper barrel-cylinder gap.
This requires a special (expensive) tool that works down the bore to precision cut the rear of the barrel.
Last, a different barrel, especially one that's had to be trimmed will need to have the forcing cone re-cut and precision gaged with a drop-in plug gage.
The forcing cone is CRITICAL to good accuracy and safety.
This requires another tool that works down the bore to re-cut the cone, and a brass lapping head to lap the cut smooth, plus the precision gage to make sure the cone is the correct diameter.
All this costs considerable money and you better know exactly what you're doing. This is why it's cheaper to have barrel work done by a pro who has the tooling.
Want to run a high risk of ruining the gun?
Use the hammer handle through the frame to remove and install the barrel.
You may notice a "POP" sound as the frame cracks, or feel an odd sensation as the frame bends.
If/when the barrel doesn't screw on with the right amount of torque and the front sight is off, either stick a home-made washer on the barrel, use a file to try to cut back the barrel shoulder leaving some nice gaps from the uneven shoulder, or as I've seen before, file the front of the frame. Don't worry, you can fix that with some cold blue.
To set the barrel-cylinder gap, use a file to hand file the rear of the barrel. Of course it won't be even, but what the heck.
Then just ignore the forcing cone.
Last, when you shoot it, wonder why it doesn't shoot as good as it did, and why it's spitting bullet metal out the gap.
