I'm not sure about your .40 cal. concerns but the US gov. will not allow any components except maybe shotgun supplies, to be shipped out of the US. This is a Homeland security thing and we are in the same boat here in Kanada, we cannot bring anything like that out of the USA. It is believed by some in that gov. that the components could be used against the USA. 
  The only thing that I agree on is the fact that Kanada has let most anybody into the country including many terrorists, that could then try to enter the US.

mick,
i also have a 0.400 bore in my 40/72.
what is suggested is that you get your paper and measure what 4 wraps add to the diameter of say a bolt or a bullet if you have one.
if you are going to wrap wet, do it that way and measure when dry.
from experience, the baco 9 lb paper i have adds 0.0065 to a bullet.
if you subtrat this from 0.400, you get 0.3935.
a 0.393 bullet will work ok and will suit blowtubing as it will be a little small.
a 0.394 bullet will be harder to chamber the round, but will most likely be more accurate. it will require good wiping and a dry bore.
the best accuracy comes from the fattest bullet and the thinnest paper that makes 0.400 and works.
many have found that seth cole 8 lb 55w works well.
it will add 0.005 to a bullet when wrapped wet.
you can get it from art supply warehouse and they will send to oz for fair postage rates.
my chamber is a greaser one, and I have had a mould made that patches to groove diameter for the part in the case, and bore diameter for the part in the bore.
no greaser can match it for accuracy, and I use it when testing greasers as a control.
if you go this way, you only need 0.2 to 0.250 at patch to groove diameter.
such bullets can be finger seated in fired cases with no sizing.
if you have a freebore chamber, you could make the larger diameter to that length plus however much you want in the case, which would ideally be 0.100 to 0.150.
my mould was custom made by rick at kal moulds, and has an elliptical nose 1.5 calibres long.
it shoots well out to 1000 yards and bullets are usually cast at 12:1 or 14:1.
they fully bump up to the ogive, but no more at that alloy.
they shoot with a little less drop at 200 and 300 yds than 16:1. and a full 7 points flatter at 900 and 1000 yds.
this translates to less wind deflection.
if you want to breech seat, a straight sided bullet is easiest.
I currently have a baco 0.396 bullet that patches to 0.401 with 8 lb seth cole, and breech seat with a palm seater o.k.
when I found the right airgap that bullet shoots 10 shot groups  about 3/4".
keep safe,
bruce.

Y'all also need to make sure you enter in brass neck thickness into the equation.

Roselle tracing paper at 0.00175 or so, and a 
DD bullet at 0.401 at base and stepping down to 0.395"
works well for me.
the other factory is the twist of your barrel. 
If 16 twist, go for a bullet about 1.325" long.
Mine is that length, and works very well out of my 40-65
16 twist rifle. Will even stabilize and shoot well out to long range.
Need to find my bullet PICs, and will post.
beltfed/arnie

Number 1535 is my DDEPP(DoubleDiameterEllipticalPP) bullet for 16 twist 40s
1.325" long, about 373 gr in my 9+1 ww/lino alloy.
In my 40-65,  74.5 gr Swiss 1.5 under it gives 1400fps
over my Oehler 33.
Group at 100yds 
Number 1527 shows also my other 40 a 40-72
with my straight sided 0.395" dia x 1.55" Elliptical PP bullet
patched with the Roselle paper, it is a snug sliding fit into my
12 twist Douglas barrel. The long gg is my BFSS 460gr 1.55" long.
on right is my 40-65s,  the DDEPP, my Elliptical minigroove
that shoots extremely well(a 99-4/100 at 800yds)
and a Lyman Snover for comparison.
beltfed/arnie

arnie,
i should have got a 12 twist in my 40/72 instead of the 13 twist i have.
all is good in hindsight!
i thought  the 13 would shoot bullets of 1.55 long, and it does, but they have a slight wobble as reported by pit crew at 600 to 700 meters, then go stable again.
i had to go to a 1.5 bullet to avoid that, 3 bullet moulds later.
just goes to show that the accepted stability factor of 1.5 is a joke for long range work.
keep safe,
bruce.

mick.
i can breech seat 0.401 with a palm seater, and suspect that 0.402 would be doable with a weber.
alloy hardness can effect ease of breech seating.
your other option is to get som seth cole 8 lb 55w mentioned above which will add 0.005, giving you 0.400 from a 0.395 bullet.
i just ordered 2 rolls, and it cost me aus$ 22.00.
0.400 bullet in a 0.400 bore will have a nice friction fit.
if you have freebore, you might do well to consider patched to groove in a parallel sided bullet.
it does not get much better than the groups you have shot, however you load ammo or what bullet you use.
where the pp bullet is superior is when there is air movement.
assuming that the pp and the gg bullets can group the same in a deadwind condition, and that they have a similar drag nose, the pp bullet will tend to have less width in its groups as wind deflection becomes an issue due to the drag of grease grooves.
this will translate into a few more points for score, or just plain smaller groups if that is the goal.
it could be worth contacting baco with a request that the shorter bullet be made at the diameter you require. nothing to lose.
keep safe,
bruce.