Why do you feel you need a 28"+ barrel. A CVA Optima V2 26" barrel is stainless and the rifle weighs under 7lbs. 2" more barrel will be lucky to add another 50fps, probably more like 36-40fps. They cost about $260 at muzzle-loaders.com.
https://www.muzzle-loaders.com/rifle...brand_model=21
What do you mean by re-machined like the Accura?