L1A1 Blank Firing Question.

[Bruce_in_Oz]

It gets a bit tricky.

Blanks are blanks because there is no bullet.

This means that there is no significant resistance to the gas expanding up the barrel.

It is also the reason that blanks are loaded with VERY fast-burning powders.

To burn correctly, "proper" rifle propellant REQUIRES the mass of the bullet and the initial resistance of that bullet entering the rifling.

The BFA bore "restrictor" contains MOST of the gas within the barrel and this is directed through the gas port. Then, the regulator ( say, on an L1A1 type), VENTS excess gas and the remainder hammers the piston back a very short distance, but with sufficient force that is transferred to the breech-block carrier, and away we go.

If you are firing BRASS blanks, and the regulator is not set to correctly bleed the excess pressure, the "return wave" will often travel back to the chamber and partially crush the blank casing. Something similar happens to those horrible plastic blanks.

Pressure curves, dwell times and residual bore pressure at extraction are VERY different between ball, and that of blank fired with a bore restrictor fitted. The residual bore pressure factor, coupled with their VERY fast bolt movement, is why you need a "blank-firing shield" with the open-topped action of the M-14; to avoid a face-full of partially burnt powder residue