I have fired thousands of these Simunition 5.56mm cartridges. As stated, their intent is for use in force-on-force training, i.e., people shooting at each other. The people involved must be appropriately clad with heavy clothing and face protection. For use in, typically, M16/M4-type weapons, the standard bolt/carrier assembly is replaced with a apecial blowback bolt. When fired, the back (brass part) of the two-part case telescopes rearward under pressure and provides impulse to the bolt, allowing the weapon to function normally in semi-auto and full auto modes. The blowback bolt is designed in such a way that ball ammunition cannot be used with it, because it will admit only the slightly smaller rim diameter of the Simunition casing. The plastic projectile actually contains not paint, but a colored soft soap. It leaves a small flower-shaped marking upon impact. The nose of the projectile is scored for ease of opening upon impact. Different colors are necessary to determine who did the firing, and each participant in the melee is issued a different color.
For military use, this 5.56mm ammunition was also available linked for use in the M249 (FN Minimi), also with a special blowback bolt. It functions very well in the M249 in full automatic. Same is true with the M16/M4. Firing noise is very quiet, sort of like a BB gun. Simunition also made a similar round in 9mm for pistols, in both marking and blank configurations. Special non-recoiling barrels are used for these, which are/were available for a number of different pistols.
As I remember, there is a small propellant charge used (just a couple of grains), and I believe that it differs in amount between the rifle version and the linked M249 version of the 5.56mm.
I have fired this 5.56mm ammunition in a conventional bolt-action rifle, but the cartridge headspace is a little greater than standard, so the bolt is difficult to close. I do not recommend it. Accuracy is nothing to write home about, but the intended use is for very close range, maybe 20 yards at most.
I wrote up a fairly extensive test report on this ammunition 8 or 9 years ago, but it’s probably on one of my archived hard drives. Maybe I can find it if anyone is interested.
One additional item I had forgotten. The 5.56mm Simunition rifle rounds were packed 20 per box, composed of two blue plastic chargers (or clips, if you prefer) holding 10 rounds each. If there is an adapter available allowing the chargers to feed into the M16 box magazine, I have never seen it. I don’t believe the normal magazine clip adapter used for the metal clips would work, but I have not tried it.
Also, periodic cleaning of the weapon’s bore frequently is essential, as plastic from the projectile builds up after awhile, and I have seen projectiles stick in the bore when cleaning is not performed frequently enough.
There is another similar-but-different marking round that was available in both 5.56mm and 9mm, named UTM (for Universal Training Munition, I think) that originated in South Africa. My experiences with it were not so good. Projectiles could stick in the bore and COULD NOT be removed. That happened a few times. It was a completely different projectile design, made partially of Aluminum. Possibly this problem has been solved if UTM is still on the market. I seem to remember that the “paint” used by UTM was a type of colored cosmetic wax.
I still have a variety of Simunition and UTM ammo in all configurations, some of which I have not mentioned, laying around in my garage.