I am shooting an ASSRA indoor match shortly and using a .25-20 Winchester using cast bullets (87 grain). The range requires the centerfire loads to be "squib", which it defines as subsonic. The slowest 87 grain load I've managed to find is 3.6 grains of Red Dot, from the Lyman Cast Bullet Loading Handbook. The indication is that the load is still in the 1150 fps range, which is supersonic, in a 24 inch barrel. My single shot has a 26 inch barrel, which probably adds 25-30 fps to the velocity.
I've been reloading for a while, but have never had much of a sense of adventure doing so and have a healthy aversion to loads not reflected in a lab tested manual. In this case, the issue is more of too little than too much, but I've no interest in finding a bullet lodged in the barrel for lack of sufficient powder.
Can anyone recommend a subsonic load for this cartridge that's been lab tested and published?