Grump, I've got a Black Diamond and, until a year or so ago, could not get consistently good accuracy out of it. In the process of trying to solve a different problem in a different gun, I stumbled on a loading technique that I haven't seen or heard of being used anywhere...though I'm sure someone, somewhere must've tried it sometime. It really helped the Black Diamond and, though it didn't turn it into an MOA shooter, 2 to 4 inch groups at 100 yds for strings of 15 to 20 shoots without cleaning were the result. There are a couple of caveats:
1) The process is a bit involved, it's a pain in the field and best avoided if you're reloading in a hurry. It may a bit hard for me to describe as well.
2) This may be a bad idea...that may explain why you don't read of it. I only know it works for me and hasn't damaged any of the rifles I've used it in, over at least a couple of hundred shots. It's been used in the Black Diamond, a Black Mountain Magnum, a Greyhawk, a T/C Hawken, a System 1 .50 and a System 1 .58. It's been used with Maxi's, Mini's, Black Belt Bullets and sabots.
What you'll need for each load:
1) Crisco - the secret ingredient...even for sabots!
2) a tight fitting jag
3) a dry, clean patch - I use baby wipes, the kind you buy at the store for about $2.79 a box pre-moistened....except I open the box to let them dry out and then cut to twice the size of a normal .50 cleaning patch. I then fold the B-wipe patch over to use a double thickness.
4) 90 to 100 gr. of loose Pyrodex RS. 90 gr. is best for accuracy, anything over 110 grains gives poor accuracy due to fouling. Pyrodex pellets seem to foul more than RS even in equivalent weights. This approach will work with two 50gr. pellets, but the # shots between cleanings will be about 8 to 10 instead of 15 to 20.
5) Conical bullet of choice - this may be a Maxi, Black Belt Bullet, or sabot loaded with a handgun bullet. If shooting sabots, I use the T/C Mag Express sabot.
Other stuff might work as well or better...but this is what I use.
Loading-
After dumping your powder charge down the barrel:
1)Smear a little Crisco on the outside of the projectile or sabot, maybe a little in its base as well. Not much, just enough to make it feel slick.
2)If shooting sabots, 'pre-splay' the petals of the sabot. Fold the petals back about as far as you can, place the sabot face down on a flat surface and push hard on its base until the petals take a bit of a set away from the sabot centerline. This predisposes the sabot to opening quickly on leaving the muzzle and separating from the bullet. Pre-splaying of sabots could be done at home.
3)Start the projectile in the barrel BUT LEAVE TIP OF BULLET NOSE LEVEL WITH MUZZLE.
4)Fill the space between the bullet tip and the inside of the bore AT THE MUZZLE with a ring of Crisco. Now this is critical and hard to describe: Don't 'pack' ALL the space between the bullet and the inside of the bore with Crisco, just fill the area between the bullet nose and the inside of the bore AT THE MUZZLE with Crisco. If you 'pack' the Crisco in, you'll have too much; the bore will get sloppy and accuracy won't be so good. Use just enough Crisco to form a continuous ring of the stuff around the bullet nose at the muzzle.
5)Place jag on ramrod and dry patch on jag
6)Seat the bullet using the patched jag. Use uniform seating pressure when bullet reaches powder. Use only ONE stroke in (the seating stroke) and ONE stroke out (to remove ramrod). Resist the temptation to work the patch up and down a few extra strokes...it just introduces more variables and hurts accuracy.
7)BE VERY CAREFUL WHEN WITHDRAWING THE RAMROD. YOU'LL BE PULLING A VACUUM IN THE BORE AND IT WILL TRY TO SUCK THE PATCH INTO THE BORE WHEN THE JAG CLEARS THE MUZZLE. If it does suck the patch in DO NOT TRY TO SHOOT IT OUT! It's a bore obstruction that could bulge the barrel. If the patch gets sucked in, you'll have to fish it out with the Worm. Cutting the patch a little oversize seems to minimize this problem.
There you have it. Besides improving accuracy, this technique makes loading much easier and prevents the un-plated lead Black Belt Bullets from leading up the bore. It also greatly reduced the 'first shot flyer out of a clean barrel' problem. It's worked well in everything I've tried it in. But use your judgement...no one with any official standing has ever blessed this loading technique. If you see something risky or doubtful about it, don't use it. Much better to play it safe, especially if the gun belongs to someone else.
Good Luck.
Bob Young