I thought I read in this forum a while back that a few guys would load powder into their muzzleloader with no projectile and fire it off into the air on the 4th of July.
What would happen? Is it dangerous? crazy?
A guy here at work was talking about it yesterday and asked me if I had done it.
I let him know I didn't but would get your guys opinions. I wouldn't do it, I have better use for my gun but I just wanted to ask so I could let him know if it was something that may cause him an issue.

No - it's not crazy. I have a White Ultra Mag, and the manual suggests firing a "squibb load" before shooting to foul the barrel. This is about 50 gr of powder with no bullet or anything else.
It goes, "Pfooooof!" I wouldn't think it would be much fun on the 4th - nobody more than a ccouple hundred feet away would hear it.
Then, you gotta clean it

IM jaybe

Well a squib load can get loud if you run a wad on top of it to compress it a little. Personally if you are going to shoot do it a safe manner on a range. Leave the fireworks to professionals.

My guess is that if you do this in the city/town, you will have an officer there in no time and you will have a little e'splaining to do.

That was my first reaction when he asked me

There are enough cases of real bullets being shot into the air and landing with bad consequences that anyone seeing someone shooting into the air would and probably should report it to the local law which is a thing you do not want to have to deal with. The other thing is that less informed people and children could view this as a "safe"/"normal" activity which is another thing we don't want to encourage.

Why would it be dangerous? You're going to get a lot lower pressures withouta bullet in the barrel! I suppose it could start a fire, if pointed wrong!!

The only time I did this, on one 4th of July, I put 200 grains of FFFg into a heavy-barreled .36 cal. percussion rifle and shot it up into the air. It made one helluva muzzle blast/flash, and brought the neighbors out of their houses for a couple of blocks in both directions. After three or four shots, the barrel was crudded up worse than if I had been shooting balls in it! But it did make a good display. The only thing that would have been better would have been to use a Brown Bess or Charleville musket of the Revolution period - more authentic, you know!

Note that I did this in a rural area in Texas where most neighbors had personal shooting ranges in their pastures,and no one thought much about a few rounds being fired off from time to time, except on Sunday morning, or course.