I don't know if you've read the controversial thread that's going on right now about dry firing, and that's not what this post is about. It's just that I have come up with some questions about the practice of dry firing.

Does anyone here do it for practice?
Is it hard on a gun's firing pin or other mechanisms?
In terms of safety, would loading in a spent cartridge be advisable?
Could the use of a spent cartridge protect the firing pin, etc., from potential damage?
How about loading a spent primer on my inline muzzleloader?

From what I've been told, dry firing will not harm relativley "new" guns. I don't know how old a gun has to be for it to be a concern.

There are products out there that are essentially dummy rounds, that are made for dryfiring. You can make one easily by depriming a spent cartridge, drilling a hole through the side, and then installing a pencil eraser in the primer pocket. Trim as necessary.

I know a few gunsmiths who tell me dry firing will do no harm to a gun. When I was in the military dry firing was a mandatory practice. The instructors are some of the best shooters in the world. I don't care what anyone says.

should cause no problems on a modern gun in good shape
If it bothers you just get yourself a snap cap or make one with spent shells and a small bit of strong rubber plugged into the flashhole

Depends on the gun. Rimfires, as a group, don't take dry firing well. The firing pin usually impacts the chamber wall and raises a burr that interferes with chambering.
Most modern centerfire guns will easily take a moderate amount of dry firing with no harm whatsoever. Other will suffer burrs and other nastys when you get into the thousands of cycles.
Don't know about inline muzzleloaders and dry firing, but a traditional percussion gun should not be dry fired. The hammer will peen over the nipple, in most cases.
You can make your own snap caps from an empty cartridge case. Deprime it, and fill the primer pocket with silicon rubber. When the rubber is cured, cut it flush with the case head with a razor blade. Good for a moderate amount of dry firing. When the rubber starts showing wear, pry it out and replace it.
BTW, when Ruger introduced the Blackhawk single action revolver, I understand that a display fixture that cocked and fired the gun was part of the sales display at an NRA convention. It snapped the gun continuously for about four days, to demonstrate that Rugers could take dry firing.

Dry firing will not cause any harm to most guns. There are some guns that I would not dry fire like old first generation single action armys. Basically if they were made in the very early 1900's or 1800's before good heat treating processes I would not dry fire them. Also do not dry fire rim fire guns. The firing pin is not centered and will strike the breech face and cause damage to it.

If you take your gun to a gunsmith to get work done, no matter how minor, it will get dry fired many times while he performs safety checks and such.

A shot primer does nothing to sushon the firing pin. The indentation is already there so what is the firing pin going to hit? Nothing.

Dry fire away. I dry fire all of my guns.

I agree with those that say dry firing won't harm modern guns. Except.... if the firing pin is part of the hammer, like on some S&W revolvers, it's a major no-no. That "floating firing pin" can be seriously damaged. If the firing pin is in the frame, like on Ruger, Colt, and some of the newer model Smiths, then it's okay because they strike nothing when dry fired.

If you're nervous about it, get some snap caps. They are cheap insurance. I would prefer them over a spent cartridge too. That spent primer can be awfully hard. Those that suggested rubber or erasers in the primer hole are right on.

I've dry fired my Glock hundreds of times practicing trigger control, with no sign or wear at all. I started using snap-caps, but because the striker must be pre-cocked by at least partially cycling the slide to the rear the snap caps were a PITA. If I accidently moved the slide back too far the snapcap would fall out of the magazine well or get caught between the slide face and the breech. Too much hassel, so I just dry fire without now.

I remember reading an atricle about competitive pistol shooting (either IDPA or IPSC, can't remember) that said that it's recommended that one dry fire at least one to two times as many rounds as they fire live rounds so that trigger control is second nature. It makes sense to me, so I do dry fire practice a lot with my pistol.

Mike

Ive came up with an answer that will protect your gun and allow you to practice squeezing the trigger. I take the brass from the gun I plan on practicing with. Push out the old primer and replace it with a cross section from an "O" ring that fits snug where the primer goes (bigger primers Ive cut pieces from garden hose gaskets). You can put the empty brass in, snap the trigger how ever many times you want, and you will not damage your gun.

I forgot to mention, you usually need to resize the brass, I even put a cheap bullet in them form my autos.

Won't hurt a thing if its a quality firearm. Even quality rimfires have a firing pin stop in them to keep the pin from contacting the breech face.

Only gun that I ever harmed by dryfiring was a yugo mauser- dry firing the rifle twice caused the shoulder on the firing pin to be peened back and the safety no longer would work. The rifle was probably unsafe to shoot in the first place- the receiver is very soft, and workmanship on quality on the rifle is very poor.