c sharps high wall slugged at .4085 groove dia with a green mountain 18 twist barrel,   want to shoot bp silhouette, gong matches.   Any bullet suggestions?  thanks in advance

The RCBS 400 CSA is a good bullet. Buffalo Arms has a number of good bullet moulds from 390- 415 grains as well. 20-1 will be a good place to start.
I like 62 grs. of OE 2f with a .030 fiber wad with grease groove bullets, and 64 grains with paper patch in our CSA Hiwall in 40-65, using starline cases.

critter68, 
first of all are you sure that is not a 16 twist GM barrel?

second, if it is indeed an 18 twist, Jim Kluskens aka DT
has a bullet that he cut for his actual 18 twist 40-65 for
Sillywet. It is 1.25" long for full stability in 18 twist.
He is having good luck with in for BPCR Silhouette 
Indeed, the 410663(about 1.38-1.39" long, is a good bullet out to 600 yds in a 
16 twist barrel 40 cal. I, too like silver had it shooting quite well in my former Brg BPCR rifles, and then in my custom HiWall.
However, I designed a couple of  1.325" long bullets that are
stabile and accurate out to 1000yds, as in down at Lodi LR
matches. One is 370 Elliptical Minigroove cut for me by Steve Brooks and the other is a 371 gr dual diameter elliptical Paper Patch that is shooting lights out in my 16 twist 40-65.  These designs could easily be shortened to
1.25" long for 18 twist.
Oh, I, too live in WI.  near Stevens Point. Where are you from.  If you are not already "on the lists" for BPCR in WI,
send me a PM with your name/email and I will get you on our list for announced shoots
beltfed/arnie

I've had great results with both the RCBS 300 CSA, and the 350 CSA. Both work well out to extremely long distance in my Rolling Block in .40-65 with a Green Mountain 1:16" twist. 
I didn't know GM offered a .40 caliber barrel in 1:18" twist? Thought the choices were either 1:16" or 1:14" for their .40's?

You might like to try the BACO 400 gr Money Bullet #JIM409400M4 this seems to work well in my 40/65 which has a GM barrel. Just as a matter of interest my load is 61 gr of Wano a .020 card wad and the Federal 155 LMP primers seated through newspaper. YMMV.
Mike.

talk to Steve Brooks about a 405 gr slug    i like mine in a GM barrel

I started out with the Saco 740 mold  in my wife's 40-65 Shiloh Sharps and it shoots well.  Went to a Paul Jones Creedmoor that drops out about a 418 gr. bullet with 30:1.  Can't get the Paul Jones molds anymore  but BACO, Sagebrush, or Brooks make a similar Creedmoor.  The load behind both bullets is 51 gr. 3F Swiss, .030 poly wad with .002 newspaper on top, Fed. 150 primer.  For the long targets at gong matches we duplex the 40-65 with 4.5 gr. of Reloader #7, and 45 gr of 3f Swiss, Fed. 150 primer, .030 poly wad, .002 newspaper on top.  These shoot really well in the wife's rifle and she won the Quigley Match in 2002 with this combination.
Greg

I have had best results with R.C.B.S 350-360 grain flat nose in 18 twist.  Vic.