There is no such thing as an "optimum" length, it depends on the use. I loved my 14" .45-70 Contender, it was the perfect 'hammer' handgun. My 16" Contender carbine is super handy in tight quarters. My 34" rollingblock is the best for long range shooting with iron sights. Ballistically there isn't enough difference to matter between 22" and 30". What are you going to do with the rifle - that will determine the "optimum" length.
Excellent custom barrels are made by Bullberry, MGM, OTT, SSK and a few others.
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