How long does a barrel need to be to be efficient?

[RyanJames170]

I have nothing to back my opinion but I believe the grade of powder would make more than a little difference - Fg likely take full advantage of the extra barrel length - some old feller told me once that each G was worth about six inches of barrel (dont remember who he was or where) it kinda made sense
I know nothing of substitutes - bought a can of pyrodex one time - fired a few shots and sold it to a bloke I didnt like.........................

I could agree that that might be true, it would be a interesting thing to actually test

[perotter]

To be efficient 24" would be good for being efficicient. One of 20" is a bit short for getting range. Based on historical data and use.

The question is efficient and not optimized length.

One historical point of practical use was the Westley Richards used by the Boers. They found 24" barrels the best overall. Good enough to to cause a up to a 40 to 1 kill ratio against the British army in the 1st Boer War. The Brits had long barrelled Martini-Henry's.

In the last battle the Boers killed 92 Brits with 78 of the kills being head shots. So the 24" barrel proved to be both accurate and provide enough power to do the job.