The best offhand shots in the world shoot guns with muzzle weight. Muzzle weight means the gun balances forward of the lock area or where the offhand supports the stock. Muzzle weight helps the gun 'hang' steady on the target. Good offhand shooting requires some muscle toning and practise to do well. What feels heavy now, probably won't after 6 months of pactise and you'll want even more muzzle weight. Body structure and strength throughout the body pretty much dictates what we prefer and most people want something different.
Gun weight and weight distribution is very subjective. Suffice to say, 'feel' a variety of guns and use what feels best to you.
A short gun with thick barrel walls can hold as well as a very long rifle with heavy swamped barrel - the 'feel' is identical and the shorter the gun, the less 'barrel' time the ball has, so thus has greater accuracy potential due to less gun movement prior to the ball's departure or less need for extended followthrough - offset somewhat by the longer barrel's sight radius which should give advantage to barrel length - it's all tradeoffs. Good muscle tone in arms, shoulders and back promote better offhand shooting - THAt is a given.
Harry Pope, famed barrel maker and Scheutzen-competition shooter once said that a Man's offhand rifle should weigh 16 pounds and a women's offhand rifle should weigh 12 pounds. No hooks, no plam rests today on our muzzleloaders and indeed, some offhand competitions will not allow body resting an elbow, all this changes what a person can handle - but - muzzle weight within a person's strength and build is usually necessary to do well.
Try a bunch and pick what's best- for you.
