[Alpo]

I’ll take a stab at it.

The powder is not “expanding and cooling” in its trip down the barrel. It is burning constantly, producing more gas, which means more pressure, which means faster bullet.

That’s why a bullet from a longer barrel is faster than one from a shorter barrel. Longer barrel time means more gas pressure.

The BANG at the end is the unburned powder all going off at once, when it hits the oxygen at the end of the barrel. While it is in the barrel it is burning at a specific speed. This speed depends on how the powder was made. You are aware, aren’t you, that powders have different burning rates?

The BANG from a 2” barrel is louder than one from a 6” barrel, because less powder was burned in the shorter tube, so more went off all at once.

If you take a silenced 22 automatic pistol, and shoot the entire magazine, it sounds like this: POP pop pop pop pop pop pop pop pop pop. The first round is louder than the others. That’s because the silencer is full of oxygen for the first shot. For the rest of the magazine the can is full of burned powder gases. But, after shooting that mag empty, if you stop and reload it, when you shoot again, it will sound like POP pop pop pop pop pop pop pop pop pop. That’s because during the time it took to reload the magazine, the burned gases were replaced with oxygen, again. If, however, you spray nitrogen down the barrel, before firing the first round, there is no “First Round Pop”. They all sound the same.

Now, for the second part of your statement.

Yes, if you attach a 2-litre bottle to the muzzle of your gun, and it is a low-powered gun, it will work for a few shots. The plastic bottle will act like the baffles in the can and collect the powder gases, and allow them to bleed off slowly and quietly. Until you have shot the bottom out of the bottle. Each shot will be progressively louder as a bigger hole appears allowing more oxygen into the bottle.

If, however, you attach your 2-liter bottle to a high-powered gun, like a 223, the first shot will blow the bottom of the bottle out, and you will have accomplished nothing.

Well, that’s not quite right. You will have accomplished one thing. You will have committed a major federal felony. As soon as you put that bottle on that barrel, you have made an unregistered silencer. Good for 10 years at Club Fed and a 250,000-dollar fine. It doesn’t even have to work. Stick a potato on the end of your gun and you have made an unregistered silencer. Attempting to muffle the noise of a firearm, even if you don’t succeed, is the same crime as making a good one.

If you want a quiet gun, you have two good choices. Get a long barrel and load specifically for it. 24” barrel with a light powder charge and you can get awful quiet, for shooting blue jays in the back yard. Or, buy a registered silencer. Jump through the government hoops and pay the big bucks. ‘Cause friends and neighbors, six hundred dollars for a licensed can beats the HELL out of a quarter million dollar fine.