I don't know anyone who has used them but just as an FYI a HBWC would only be legal if it protrudes from the mouth of the case. I'll paste the information from page 12 of the SASS shooters hand book below.
SINGLE ACTION SHOOTING SOCIETY
Shooters Handbook
~12~
Copyright © Single Action Shooting Society, Inc 2015
Version 20.2
AMMUNITION
The minimum standard for center-fire ammunition used in all smokeless categories in all SASS
matches State, Regional, National, International, and World Championship Competitions is not
less than a minimum power factor of 60 and no velocity may be less than 400 fps. The
maximum velocity standard for revolvers is 1000 fps. The maximum velocity standard for rifles
is 1400 fps. Pocket pistols, derringers, and long-range rifles are exempt from the power factor
and velocity requirements.
Power factors are simply calculated by multiplying the bullet weight times the velocity and then
the resulting number is divided by 1000. Some examples are as follows:
100 gr bullet traveling at 600 fps has a power factor of 60: (100x600)/1000=60.00
77 gr bullet traveling at 800 fps has a power factor of 61.6 (77x800)/1000=61.60
200 gr bullet traveling at 400 fps has a power factor of 80 (200x400)/1000=80.00
• Shooters may be held responsible for damage caused to a target or injury to personnel due to
“bounce back” because of inappropriate ammunition. This major safety violation is grounds
for “instant disqualification” and ejection from the match.
• Revolver and rifle ammunition may not be jacketed, semi-jacketed, plated, gas checked, or
copper washed. It must be all lead. Molydisulfide, polymer coated bullets, or equivalent
are acceptable.
• Revolver and rifle ammunition must be of “single projectile” design. “Multiple projectile”
bullets are illegal.
• Ammunition with bullets recessed below the case mouth is disallowed.
• Throughout this manual, blackpowder means blackpowder, or a blackpowder substitute such
as Pyrodex, 777, APP, or comparable propellants intended for muzzle loading firearms.
Propellants containing nitrocellulose are prohibited as blackpowder substitutes. Any
combination of smokeless and blackpowder (so called duplex loads) is specifically
prohibited.
• Shotgun shot size must be number 4 lead birdshot or smaller for all events (no steel or
plated shot).
• Magnum and high velocity shotgun shell loads are not allowed.
• Shotgun shells shall not be sized down by the use of any die not manufactured for the
specific gauge.
• Shotgun Shell shall not be scored (ringed) as to cause the shot-shell case, wad, and shot
column to be shot from the firearm as one projectile.
• Pump and lever action shotguns are allowed to load no more than two live rounds at a time
in the main match stages unless specified in the stage description. In team events, shotguns
may be loaded to their maximum magazine capacity.
• All centerfire or rimfire ammunition must be designed to package the bullet, gunpowder,
and primer into a single metallic case precisely made to fit the firing chamber of the firearm.
The primer must be of the type that uses only a small charge of impact sensitive chemical
that may be located at the center of the case head or at its rim. Electrically fired ammunition
is illegal.
