Hi floridaboy,
For a New Service chambered in .455 Eley, I see no reason why you could not simply refer to and use .45 Long Colt Loadings, if avoiding those which are 'Ruger Only', of course.
.455 Eley, used a .454 Bullet.
.45 Long Colt...generally uses or used a 454 Bullet...
The only difference between .455 Eley and .45 Long Colt, for present purposes, is Cartridge Case Length and thus Cartridge Case Capacity.
And in Smokeless propellents, the Case Capacity being less, should not be an issue unless using very bulky Powders.
If this were a Webley Revolver, it would be a different story, oweing to the Webley being at the limits of it's durable strength with standard .455 Loadings.
The Colt 'New Service' is a much stronger design, normally chambered in .45 Long Colt, and, of course, available in it's day, in other less powerful Cartridges, and even .357 Magnum ( being about equal in power or stress for the Revolver to the .45 LC ) toward the end.
Bullesye, while an old and venerated Powder, always seemed a little 'sudden' to me, especially for any long Barrels or large Calibers.
I am not up on what Powders would be good to investigate for .45 LC, but, I would say in general terms, consider the Powder candidates according to your Barrel Length, and, the Bullet weight you intend...and, of course, stay with Pure Lead for this, or, at most, a very soft Alloy.
If for Plinking and Target fun, 'Trailboss' may be worth considering.
"777" may be a good one also, for plinking or Target.
I do not know what the best Powder candidates may be for Hunting or Self Defence use...being then of course, calculated to be of full power for this Arm.
I hope to be learning more about Powder Candidates for .45 LC since I am intending to be loading for it soon myself, for my New Service, and, for a repro Colt 'Bisley' Long Barrel.
Post a picture of your Colt..!