From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Flash Tubes
Organization: Hewlett-Packard Fort Collins Site

Some years ago, a few highpower competitors felt the powder burning could
be improved if it was first ignited next to the bullet.  The reasoning
was that much less unburned powder would be pushed into the barrel.
Barrel life would probably be increased and accuracy might be better.
After all, many large caliber military rounds benefited from flash tubes.

Brass tubes about 1.25-in. long with an inside diameter of about .080-in.
and outside diameter of a No. 6 screw were used.  The case's flash hole
was drilled and tapped to 6-48.  Flash tubes had one end threaded just
enough to let it tighten up flush with the primer pocket's bottom.  Then
the flash tube was screwed into the case from the front using a pin vise.
Any flash tube protrusion into the primer pocked was easily removed with
a primer pocket uniformer.

Decapping was done with a steel pin long enough to go through the flash
tube from the front.  It took some care to ensure the decapping pin went
straight into the flash tube's front end, but it worked.  Decapping was
done by placing the fired case on a plate, then inserting the decapping
pin into the flash tube, finally tapping it to push out the primer.  A
tedious task indeed.

The results were excellent.  Seems primers with less uniformity or hotter
ignition produced groups/velocity equal to more uniform and milder ones.
Powder charges needed to be reduced about .2 to .3 grains as the flash
tube reduced internal case volume.

But flash tubes didn't last.  With proper primers, the .308 Win. shot
just as accurate without 'em.  And decapping was much easier and faster.

BB