Hepburn 40/65,
  I have acquired a pretty good order Hepburn in 40/65 . According to what I have found out it is the same as a 40/70 Sharps Straight .
  I have done a chamber cast and it is the original .403 case dimensions ( .422 neck dia ). It is 18" twist and the Groove is around .410 .
  Can anyone recommend a bullet mould for this combination ? I have ordered a set of RCBS dies from Buffalo Arms for the .403 Bullet dia.
I will be casual target shooting with this rifle so I was thinking around a 330 to 350 weight bullet . I also have the ability to swage paper patch in a Walnut Hill Press but I will have to get the dies to suite the Hepburn bore . 
Thank You  , bison-j

Saeco 640(370gr) is currently my favorite bullet for BPCR pigs (300M) and Turkeys (385M)

RCBS 82070, 300GR, SP-CSA may become an alternate favorite for at least 300Ms -- maybe 200M chickens too.

Lyman410663 (400gr) has knocked over rams at 500M than any other for me.

Suggest that you visit Buffalo Arms and Montana Bullet Works and look at the selection of 40cal plain base bullet they sell. Could be smart to order 50-100 of each that appeals to you. Shoot them up and THEN decide on your 1st mould.

Grisen

My wife shoots the Saeco 740 at about 410 Grains.. in her .40-70 SS with black powder...but, it is 16 twist...don't know if a 18 twist would stabilize that one...

Terry

Sounds to me that the rifle, with (apparently) .403 bore and that .422 neck diameter is set up for bore riding Paper Patch Bullets.
Check out the land dia of that bore. 
Choose a PP bullet say 6-7 thousandths smaller than Land dia
and then wrap with 0.00175-0.002 paper to bring up to land dia plus say0.001.
Bullets of say 20+1 lead/tin should bump up into the 0.410 grooves
For example, my 440 gr Elliptical PP bullet is at 0.395" dia
I patch up to 0.401" with Roselle Tracing paper at 0.0017" thick. Makes for a sliding fit on to the lands in my 40-72 Douglas barrel at 0.400/0.408. The rifle has no freebore, and a short leade.

beltfed/arnie

bison-j
first of all a plea.
you seem to have an old rifle in original condition.
many of these rifles have been so called "improved" by rechambering.
please do not do this.
in original form they shot well and reliably, even dirty, and were much respected.
they used bore or bore plus a little paper patched bullets, and were set up to do this with maximum efficiency.
when people went to greasers this knowledge was lost, as evidenced by some answers to your question
having an original is a fantastic opportunity to relearn this knowledge.
a bullet for that gun should be no heavier than 330 gns to remain stable in flight.
if your chamber neck is 0.422, and your necks are 0.010 thick, you will need a bullet patched to0.402 to fill that neck, but if they are thicker you will need a smaller bullet accordingly.
a bullet patched to a size that will be a sliding fit in the bore diameter (as opposed to groove diameter) is what you need to find.
shooting dirty might require a bullet a little smaller than bore diameter in conjunction with a grease wad.
the bullet does not need to be seated deep in the case.
keep safe,
bruce.

jim,
just noticed you are from the darling downs - a fellow aussi.
my friend Charles has a rifle similar to yours, so more than one has crossed the pond.
his is 5 groove, so I am unable to establish exact internal barrel dimensions.
while I have never had a dud baco mould, they don't seem to have anything that would suit your project.
kal moulds and steve brooks have supplied me with excellent moulds, as described in the order.
I believe accurate moulds are very good, but have never had one.
bruce moulds is purely a purchaser and user of moulds.
seth cole 55w tracing paper will add 0.005" to a bullet diameter when wrapped wet, and baco paper will 1dd 0.006 to 0.0065" also when patched wet.
others might advise similarly on other papers, as has beltfed.
please keep us informed as you progress.
keep safe,
bruce.

jim,
there exists a website called open library.
you can find on there books which you can read online.
one of these is called "trajectories of American hunting rifles".
it was published by forest and stream publishing in 1885.
on page 66 is the test done on a Hepburn like yours in your calibre, which you might find interesting.
when you get the book up, you click on the edge of the page to turn it.
keep safe,
bruce.

Thanks Again for the replies guys ,
Bruce your information has been a great help to me . I did read the online book that you suggested . I got my RCBS .403 dies from Buffalo Arms today but I don't have any projectiles to try yet .
One of my customers and best friends owns CBE bullet moulds . He doesn't have anything to suite my Hepburn in his cherry list . He was here this morning and tell me he buys mould handles from Kal in Canada and volunteered to order me one of his paper patch adjustable moulds in .395 diameter . He ordered it today . So I will wait for that to come . 
Kal said he could do the mould right away as he was working on the machine at that time . Otherwise it would be a while before he could do it . Jim