I don't know the specific size of the bore on the .40s, hopefully someone who has one can comment. Final patched bullet size should be just under bore diameter, such that the bullet takes little pressure to seat - you don't want to risk the patch jamming and pushing the bullet through it.  
 
Do you know your paper thickness you will be using for patching? Typical I have is about .0015", so two wraps add .006" to the diameter - my .442" bullet is .448" patched.
 
David

The Pedersoli Rep. in America, Dick Trenk, has advised that the the .40 cal Gibbs being new he currently does not have loading data for it. He does however have the following useful information:
 
"Our 40-65 cal. ctg barrels used a bore of .400" and groove .408". �We use the same specs for the .40 Gibbs. I am assuming the .40 Gibbs will use a .400" bore so PP bullets can be cast so that a PP gives .400" diameter. Figuring that the paper will add .008" that means cast a bullet .392". Remember that mfr. tolerances vary a bit so I advise to slug the barrel a few times before ordering a mould. Also you can find paper which will allow the right dia. if your casting is a little off specs.
 
"We have found good results using the Wonder Wad in the .451 Gibbs so it is worth a try in the .40 Gibbs."
 
You might also wish to contact Joe Hepsworth at www.jcunard.com. He has supplies to suit most long range muzzle loading needs and may be able to advise.
 
David

I finally gathered up all the pieces and parts and ventured off tto the range today with the Pedersoli Gibbs.  I ended up getting the Pedersoli flat base bullet mould (318 gr) and cast some 30 to 1 bullets.  I lubed them with SPG and sized to .400, a perfect fit, not too tight and not at all loose.  I used 70 gr of Schuetzen fffg.  I put a .060 stiff fiber card over powder, followed by a lubed felt wad then bullet. Started at 25 yards just to make sure I was in the ball park.  I only had to make elevation adjustments as windage was spot on.  I then moved out to 100 yrds and after some minor sight adjustments, shot a 6 shot string that was 2 1/4 inch. Nothing that would win a match but encouraging.  Being a long time "highpower" service rifle shooter, I opted for the post front sight and with these old eyes, I had trouble with the sight picture.  I know I will be getting a Hadley cup for it.  Monday I will return to the rage with the .011 front aperature sight.  I have owned several Pedersoli guns, but this rifle is head and shoulders above anything I have had in the past.  The trigger is remarkable, crisp and consistant with no creep and a great let off.  If the internals are properly hardened it should stay that way.  Regards, Peepsight

David,  My load is in the body of my message.   Peepsight

Peepsight:  
I am one of the first shooters in the US, to use the new fast twist [1 in 16"] .40 Pedersoli Gibbs in competition, at 300, 600, 800, 900 & 1,000 yards.  
Pedersoli has produced the slower twist [1 in 24"] .40 Gibbs, primarily for the European market. It is my belief, that the 318 grain .40 caliber Pedersoli mould you acquired, was designed for the slower twist rifling. Lighter bullets may shoot OK at mid-ranges, even with the faster twist. But to compete well at creedmoor distances, a 420+ grain bullet will more likely serve you better.
Shortly after receiving my F.T. .40 Gibbs from Joe Hepsworth, I had Steve Brooks make a .397" grease groove mould, which cast 438 grains, with 30:1 alloy. This bullet shoots very accurately at long range, using 80 grains of 2F Swiss powder. Velocities average right at 1345 fps, with very mild recoil.  
I am having Brooks make a new paper patch mould, to cast .390" diameter, but have not received said mould yet. Will post how new PP bullet works out. Regards, ... centershot40 [aka: volshooter2004]

Peepsight, ... all shots in the black, offhand at 100 yards, with a 12 lb muzzleloader? �I'd say that's mighty fine shooting!
You dropped your new Gibbs on concrete? That news is rather frightening ... glad to hear there was only minimal damage.  
Steve Brooks has a good website ... www.brooksmoulds.com ... you can order directly online. When I ordered mine, I asked for the Postell design ... he has many others too choose from.
My Gibbs loads? ... In all honesty, I have not tried many different loads to date. In matches, I've used either 80 grains of 2F Swiss, or 73 grains of 3F Swiss, [scale weight]. Both produce 1345 fps, across my chronograph. This load actually work well out to 1,000 yards and accuracy holds up with many .451 caliber bullets, under mild wind conditions. If I were to encounter winds past 25 mph in a match, I'd say all bets are off for the .40! But then again, we will not know for sure until we have many top shooters using the .40's in competition.
In preparation for each shot, I clean bore to the breech, using two damp patches. Load the pre-measured powder charge, through a drop tube. Place a .060" ldpe .40 caliber poly wad in bore at the muzzle, then short start it. Take a bullet [grooves are pre-lubed with BPCR Supreme] and insert it flush with the muzzle, finger pressure only. Then use my stainless steel range rod with bore guide, to ease both bullet and wad down onto the powder charge. You do not want to deform the nose of the bullet! That's basically it! Regards, ... centershot40
 

Peepsight, the bore in my Gibbs may have slightly tighter tolerances than yours. Although, ... Pedersoli is quite well known for their consistancy! I can not start a .400" bullet by normal hand pressure, even a .399" would requires manipulation and use of a short starter. Besides, it is my belief that bullets which are too snug, do not shoot as good a group consistently, as those which have a slight wiggle, when hand inserted in bore.  
Yes, I run my unsized .397" bullets, into an oversized .400" die in my Lyman 450 lubesizer, for purpose of apply the BPCR Supreme lube. This lube looks very similar to SPG, is about half the price, and comes in lubesizer type sticks. Perform a "Google" search if interested, but there is no reason not to continue using "SPG" lube! Also, try omitting the lubed felt wads from your loading process. My rifle shoots better groups without felt wads. All the best ... centershot40