www.westernstageprops.com has a wide assortment of blank types & calibers, including full, half, and quarter charges.
If you want something more than a primer or cap pop, they can provide it, along with instruction & advice on using such blanks indoors.
Can also provide several blank-firing-only replica guns in .380 & .22 BLANK calibers.
35 years ago, I worked security for a live theater while going to school.
The local opera company was putting on a production of Carmen, in which one character shot a rifle at another character.
This was on an elaborate set, characters were on opposite sides of the stage, the shootee was about ten feet above the shooter.
Original plans were to have the shooter aim his prop rifle while the stage manager fired a .30-06 blank through his own rifle off-stage.
When they were first blocking out the acts, I told the stage manager I could do better, if he & the opera director were interested.
They were.
I did.
Had an old Brazilian smoothbore percussion rifle.
Using a plastic teaspoon of old-fashioned photographic magnesium flash powder held in by a wad of magician's flash paper, it produced a very notable blast & spectacular muzzle flash for about ten feet in front of the shooter.
Inside the theater, house lights out, only stage lighting used, when that thing let loose there was no nonsense about off-stage sound effects.
Got an audience reaction every performance.
The flash paper was used as a wadding because it burns instantly & completely, with zero particulates.
The magnesium flash powder was fully consumed (tested it previous to ever taking it on stage), small enough amount to be loud, but not too loud, and ejected zero particulates.
The distance between the two characters was safe enough, but the shooter was carefully coached NOT to aim directly at his "opponent".
Today, probably would not fly.
Back then, the opera company owned no props, was glad to get the help, thought the gun's performance was magnificent, and it even passed the fire marshal.
Also supplied two single-shot percussion pistols in non-firing roles for subordinate character props.
And, there was a scene requiring one character to attack another with a knife.
Needed to be big enough to be seen in the back rows. I bought a KaBar, wire-brushed all the finish off to leave the blade bright & reflective, and ground off the cutting edge.
Scene was choreographed to reduce chances of any accidental contact.
As far as indoor blanks go, you do have to be very cautious.
BP & floral foam can still eject particulates.
Years later, built a stock of primer & foam .38 Special blanks for departmental training purposes.
Had to use some sort of wad to create back-pressure to keep the primers from backing out & binding up the revolver cylinders. (If you want to do that right, with just primer & no wad, you enlarge the flash hole a bit, but I didn't want to take the time to drill out 300 cases.)
Found in testing the foam was broken up, but would still spit & if close enough COULD hurt.
Training scenarios had to be carefully staged to prevent anybody getting stung.
Denis