Travis said "The length of the projectile protruding from the cartridge case neck of a 5.56mm Ball round and a 5.56mm Tracer round is exactly the same. The difference in the total length of the projectiles (you are correct) is considerable to compensate for the tracer element in the base of the projectile but it does not affect the distance that the projectile engages the rifling when chambered compared to a ball cartridge as they protrude from the case the same distance before they are fired. "
You are right, but you misread what i wrote, or I failed to make it clear what i was talking about.
The tracer and ball round look identical, and when chambered would have the same clearance from the rifling. After the round is fired, both rounds will move forward and engage the rifling. The primer pulse alone would probably do that. At that point the base of the ball bullet is in the case neck, which has expanded out to chamber dimensions, releasing the bullet.
IN a SAAMI minimum chamber (which I doubt is made any more) the short ball bullet will behave normally and shoot just fine.
In a SAAMI minimum chamber the base of the much longer tracer bullet is still in the case, below the neck. A SAAMI chamber neck is basically a cylinder. When the bullet hits the rifling, the unsupported and weak bullet base (the treaceer propellant sctrion) can expand, like a rivet, causeing a pressure problem.
The military solved this by making the chamber throat deeper, so that more of the bullet is in the neck before hitting the rifling, and the NATO chamber neck is tapered, to reduce the risk of riveting.
The rifle manufactures are aware of this issue and now using deeper throats to reduce risks, but tracers are still not something I would shoot in a non military chamber.
The pressure of the loaded SAAMI vs military round is not an issue. Any commercial bolt gun is as strong or stronger than a military gas gun. The difference is the ability to handle a tracer round.
