With the limited availability of many popular propellants, I picked up some Triple Seven 2F to try in cartridge loads.  Just one R&D event with a 45-70 and 405 and 345 gr slugs. The rifle was an H&R Officer’s Model.  I figured if something went wrong, that was my least expensive test vehicle.   
Following some published internet experience, I was loading 55 gr (V) with very little compression. These went off with much authority.  The ignition produced a prodigious amount of smoke, but no rotten egg after taste. 
50 yd. impact was close to my standard load. I was shooting OH so accuracy was not worth recording, but they seems to hit where I was pointing.
Years ago, I gave up BP so this was a regression of sorts. The maker’s claim quick, easy clean-up and this was an accurate statement.  Even the brass was hardly sooted.  Anyone else utilizing this propellant?  Seems like it might have a place in this sport.
My quest was locating another loading component.   
Looking for encouragement.

I use Triple 7 from time to time in cartridges.  I find it particularly useful in smaller, more primitive cartridges that need particulates to slug up undersized bullets, like .32 and .38 inside-lubricated centerfires.  Black powder does the same thing, of course, but the heavy fouling left in the bore means more cleaning than shooting.

One of these days, I will try it in my .43 Spanish rifle, which has the same problem of undersized bullet and oversized bore.  I might check it out in some of the long-for-caliber chamberings like the .22-15-60, the .25-25 and maybe the .40-3-1/4 Sharps Straight, which IME so far give mediocre results with either black or smokeless loads.

777 does seem to generate higher pressures than black powder, which might be a consideration in certain rifles, but of course the pressures don’t compare to those of a smokeless overload.

The only substitute I’ve heard of that gives mid-range accuracy comparable to black powder in cartridges is Blackhorn 209.  I haven’t tried it myself, because it’s pretty expensive, even compared to premium black powder.  But, one of these days, just to see...

I have used Triple 7 in a 500 3" BPE, (measured by volume) and it was very accurate.

Late last fall I  bought a muzzleloader to use in a muzzleloader only game unit. Now I can't get enough BH209 to even get sighted in. Bummer. I may have to use 777. Rnd ball so the loads will not be heavy. I keep hoping that BH209 will be available by hunting season. Since hunting pressure is non-existent I still shoot modern season.

Have used it twice:
* Got a load data from Hodgkin for a 170gr 30-30.  It about ripped my face off
* reload with 500gr 45-70 bullet and 52grs T7 … Five rounds shoot at 600 Yds to NRA paper.  In the 7 ring, 5 
Holes less than MOA with 3 overlaps that could have been  covered with a half dollar.  Two club witnesses and no camera