I'm gonna dredge this one back up to comment. Someone claimed that you can't overload Trailboss. I've seen other people make that claim too, but yes, you can. It's fluffy (to take up space in large cases like .45 Colt), but it's still a fast powder. Faster than Accurate No. 2, Ramshot Zip, Unique and lots of others. You probably wouldn't be able to get enough in the Super Companion chamber unless you compress it. And compressing Trail Boss is a very bad thing.
Trail Boss is not black powder, and (despite what some people seem to think) not a BP substitute. It is a fast smokeless pistol powder and should be treated as such.
Now, I'm not a naysayer on using smokeless in the Companion and Super Companion. In fact, I have done so quite a few times. But I have gone back to real black powder. Here's why:
1] Using smokeless will bend your cylinder pin. It did mine. I noticed this, and searched the Internet for tips. What I was told is that it was designed that way, to limit pressure. I don't know if that's true or not, but I do know BP doesn't bend it. I also know I don't want to have to replace the pin on a regular basis.
2] I've been told that the nipple threads are rated to about (IIRC) 17,000 psi. I'm not sure on that number, but I remember that it was lower than regular .22LR. Again IIRC, both .22LR and .22 Mag are limited to around 24,000 psi. It's kinda like using iron pipe as a 12 gauge shotgun barrel: the pipe is not rated for it, but will usually take some unknown number of rounds through it before it lets go. Bottom line is that it has worked for me and quite a few others, but there's not much safety factor.
3] Black powder ignites much more reliably than and of the smokeless powders.
And finally,
4] Black powder can perform quite well in these guns. I have Graf's (Wano) 4F, Swiss 4F, and Swiss Null B. All of those give good results, especially with alternative projectiles.
I weighed one (factory supplied, which is a Lee 0.3cc) scoop of Graf's 4F and came up with 4.5 grains. That doesn't work great with the factory 29 grain bullet, but it does with a 38 grain bullet. More on that in a minute.
I also found that with a lightweight bullet, say about 15 grains, you can fit a scoop and a half or maybe up to about 7 grains of 4F. That light bullet will scream under 7 grains of 4F.
Ok, here's where I get the bullets. 22lrreloader.com sells a .22 LR reloading kit that includes a tool. The tool is both a bullet crimper (to crimp the new bullet into the case) and a bullet mold that has two cavities. One of the cavities is a regular roundnose .22 LR bullet that weighs about 38 grains. The other is a little conical like what is in a CB Cap, and is intended for loading with a primer charge only. It weighs about 15 grains. Another source of light bullets is the Lee No. 4 Buck gang mold, that casts 18 4B round balls at a time. I have both of those molds, and use pure lead just like any other BP gun.
The 38 grain roundnose will almost but not quite fit. That can be remedied by giving each bullet a light tap with a hammer, a swipe with a file, or a snip with wire cutters. I prefer the hammer. All three methods give it a flat nose (which is good), but the hammer does it without losing any weight in the process.
That's enough for now. I'm not necessarily trying to discourage anyone from using smokeless (remember, I did it), but I did want to give a heads up on some potential problems. Also to point out that you're really not giving up much if anything, by using real black powder in them.
